integrating depthmap
TRANSCRIPT
Integrating Depthmap
A Practical Handbook for Applied Space Syntax Research
João Pinelo
September 2010
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Depthmap: Created by Alasdair Turner at UCL.
Citation: Pinelo Silva, João; 2010; Integrating Depthmap – A Practical Handbook for
Applied Space Syntax Research; Bartlett School of Graduate Studies; UCL; London.
Executive Editor: Alasdair Turner
Keywords: Space Syntax, spatial analysis, Geographic Information Systems (GIS),
Computer Aided Design (CAD), axial map, segment map, convex map, Visibility Graph
Analysis (VGA).
Version: v1 - 24/06/2010
Based on Depthmap version: 8.15.00c
http://WWW.
Copyright © 2010 João Pinelo Silva
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Abstract
Today’s research is heavily marked by the integration of information. This is achievable
by the individual and assembled analysis of different datasets. Data is often of different
types and is worked with, and stored in, different ways.
The contemporary researcher must therefore master several different software
packages that are essential to work with data. In the world of spatial or geographical
research, data is often referenced to its location. While this extends the potential for
analysis, it adds a level of complexity to working with this data.
This handbook aims at supporting the researcher of spatial and social phenomena with
the inter-software knowledge that allows the creation of the spatial representations
that are necessary to perform Space Syntax analysis, integrate its results with its
specific methodologies and with other sources of data.
The main research tool to carry out syntactic analysis is the software Depthmap. For
this reason, this handbook is organised around it. It is not a Depthmap manual, but a
guide for the options available on the way to use this central tool of space syntax
analysis and how to use it for applied Space Syntax research.
By its nature, this document is a working draft meant to be regularly updated to keep up
with the development of software, methodologies and techniques involved.
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Acknowledgments
I should like to thank all the end users of this handbook, namely the MSc researchers in
Advanced Architectural Studies at the Bartlett School of Graduate Studies with whom I
have the privilege to work with, whose worries constantly feed this work in progress.
Comments and Suggestions
The author welcomes comments and suggestions. Please do so by email to:
Disclaimer
The author makes no warranty that the information in this document is correct or up to
date.
Note that different software versions, operating systems and configurations may
conflict with certain proceedings.
Prior Reading
Depthmap Manual and Tutorials can be found at:
http://www.vr.ucl.ac.uk/depthmap/tutorials/
It is strongly recommended that you go through these Depthmap materials prior to use
this handbook. This handbook is meant to be a complement and not a replacement for
the Depthmap dedicated materials.
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Contents
Chapter 1- Introduction 9
1 A Background to this handbook 9
2 How to use this handbook 10
3 Other resources 11
Chapter 2 - Axial Analysis 13
4 Methods for creating the Axial Map 13
4.1 How to hand-draw an axial map 13
4.2 Automatically draw the axial map 13
5 Tools for drawing an axial map 14
5.1 Drawing in CAD, GIS or Depthmap 14
6 Drawing an Axial Map in CAD and integrating it in a larger map. 16
7 The CAD drawing file 17
8 Multi-scenario assessment - How to add extra value to your map while keeping it
flexible 18
8.1 Multi-scenario CAD files 18
8.2 Multi-scenario GIS files 18
9 How to export the CAD file with the axial map to Depthmap 19
10 How to export the GIS file with the axial map to Depthmap 19
11 Converting ‘any’ GIS file type to Depthmap’s GIS file format MIF 19
12 Unlinks 20
12.1 How to use unlinks 20
12.2 Manual vs. Automatic Unlinking 20
12.3 How to create a file with the unlinks of your axial map 21
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12.4 How to export the unlinks file from CAD 21
12.5 How to export the unlinks file from GIS 22
13 Links 22
13.1 How to create a link 22
14 How to import the CAD file(s) into Depthmap and convert your map into a
graph 23
15 How to import the GIS file(s) into Depthmap and convert your map into a
graph 23
16 GIS File Types - Why multi-files and its practical consequences. 24
17 How and when to import unlinks file to Depthmap 25
17.1 Importing the unlinks DXF file from CAD 25
17.2 Importing the unlinks TXT file from CAD 26
17.3 Importing the unlinks MIF/MID file from GIS 26
18 Analysing the Axial map 26
18.1 How to calculate the syntactic measures of your map 26
18.2 How to control which measure is displayed 27
18.3 How to display the table where the values of the syntactic measures are stored 27
18.4 How to display several views of the data simultaneously 27
19 Before analysing the data - Validate your axial map 28
19.1 Detecting unconnected lines 28
19.2 How to identify isolated lines 28
19.3 How to identify an island 28
20 How to export image files of maps created in Depthmap 29
21 How to correlate different variables - Scatter Plots 29
21.1 To produce a Scatter Plot 30
21.2 Correlation of a selection of elements 30
21.3 How to export image files of Scatter Plots created in Depthmap 30
22 How to export the syntactic measures to EXCEL, SPSS, JMP or GIS 31
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22.1 How to export data for statistical analysis only 32
22.2 How to export data to GIS 32
Chapter 2 - Segment Analysis 33
23 Segment map 33
23.1 From axial map to segment map (why always make axial map first) 33
23.2 Using an axial map to create a segment map 33
23.2.1 Dealing with Stubs 33
23.2.2 Analysing the segment map 33
Chapter 3 - Visibility Graph Analysis 35
24 Visibility Graph (the ‘map’ to perform visibility analysis) 35
24.1 How to prepare CAD files to VGA 35
24.2 How to prepare GIS files to VGA 36
24.3 How to export CAD files to VGA 36
24.4 How to import CAD files to VGA in Depthmap 37
24.5 Running the visibility graph analysis 37
24.5.1 Setting the grid 37
24.6 Isovists 38
24.7 Boundary Graph 39
24.8 About the grid and the graph 39
24.9 Context filling 40
Chapter 4 - Convex analysis 41
25 Convex Space 41
26 Convex map 41
27 Tools to draw the convex map 41
27.1 Drawing the convex map in Depthmap 41
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27.2 Drawing the convex map in CAD (or GIS) 42
27.2.1 The drawing file in CAD 42
27.2.2 The drawing file from GIS 42
28 Running Convex Analysis 42
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Chapter 1- Introduction
1 A Background to this handbook
Nearly 30 years old, Space Syntax has developed significantly and its level of complexity
may be felt by the novice.
As an architectural theory that actually quantifies its analysis, Space Syntax
methodologies rely heavily on methods of mathematical nature. If in one way this might
bring some uneasiness to a few students, in another way it means that, after mastering
the concepts, the calculations can be left to be dealt by computers, making it extremely
accessible to all.
Space Syntax research thus imply two complementary challenges: to master the theory
of space and society, and the methodologies that transform this in tangible results. In
order to do applied research in Space Syntax you must know how to use its central
research tool- Depthmap, and to make the most of your data input and results. This
implies the wise use of different datasets, from different sources, while making the most
of the resources.
The most powerful and versatile software to do space syntax analysis is Depthmap, and
this explains why it is used worlwide. Depthmap has been created in UCL by Alasdair
Turner, and it still being developed. The fact that it is still being developed might sound
strange, but this fact is at the core of its success. Depthmap is a very stable platform, but
it is not a complete and friendly software ready to be used by someone unfamiliar with
sapce syntax. More than anything, Depthmap is a very powerful research tool; one that
is very specific and absolutely dedicated to Space Syntax research. This is why it is kept
‘unfinished’. A looser format can constantly be adapted and keep up with research,
eventually extending it. Depthmap does not format researh, instead it lets itself be
shaped by it.This is also the reason for it to have had so many versions. It is in constant
development. New ideas are continually converted in new algorithms and readily tested
and eventually incorporated. Who knows if you will be making a contribution for it in
due time.
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Depthmap is used all around the world and it will be taught in the course. It also has a
manual. However, the experience shows that many questions emerge when students
take their first steps in practical research. The whole process involved in selecting the
sources maps, creating your own maps, calculating the syntactic measures, analysing
the data and relate it with other phenomena or data may sometimes seem
overwhelming. Of course the difficulties are overcome over time with experience,
however, in order to maximise the results of your first efforts, this handbook aims at
minimising the chances that you come to a halt. The experience from the close work
with students in previous years has been collected in this handbook. Here you will find
explanations that lead you to answers to the questions that you are more likely to face
when using Depthmap and spatial datasets that might be new for you. Because these
matters are not really a part of Depthmap, they are out of the scope of its manual,
however, they are very important and can make a real difference to your efficiency.
This handbook gives you an experienced view over research methods that will guide
you to make the most of Depthmap, your data, and your work. A part of this includes
guidance on how to keep your data organised and ready to be used, for only this way
you can make the most of it.
As a final note, I should mention that this document is ongoing work. As software
packages and methodologies develop, and students competences evolve, so does this
handbook.
Note: This hanbook inclues advice that is based on Depthmap version 8.15. However,
where relevant, alternative solutions for potential problems are presented. These
alternatives are usually solutions to issues and proceedings from the use of previous
versions.
2 How to use this handbook
This handbook is to be used as a complement to the Depthmap manual, tutorials, and
workshops. You should expect the minimum overlap between this document and the
Depthmap manual. It goes in some detail about the way Depthmap works when
relevant, but its purpose is to deal with practical issues like: how to create the data to
feed in Depthmap; how to structure it, and how to use its output by integrating it with
other data through the use of other software.
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Each chapter is organised in an order that resembles normal research steps through
topics that highlight your potential difficulties. So it is advised that you follow its steps.
Sometimes a topic may be irrelevant in your particular case, but you should make sure
of that by reading it anyway. This structure may sometimes feel that it interrupts a
smooth progression; this happens because the sequence to carry out tasks is not
arbitrary and the consequences of not explaining it at that point would make you go
back on your research, most likely invalidating some of your work.
The best way to use this hanbook is to read it once, always staring by chapter two,
which is about Axial Analysis, and then to follow it step by step making sure that you
always are one step ahead. Once you’ve read it, you will be able to use it as a guide to
clarify specific topics and inform your decisions.
You will notice that the most developed part is the second chapter, dedicated to Axial
Analysis. This happens for two reasons: a) it is the first one you will be dealing with and
so where you are more likely to face difficulties. B) Because, as you will notice, the logic
remains the same no matter the type of analysis, so the following chapters deal more
about the specificities of that particular type of analysis than with the general practices
that have been explained before. This means that if one of the following chapters does
not provide you enough information about a particular topic, you will most likely find
what you’re looking for in this second chapter.
3 Other resources
Depthmap’s website contains a great deal of relevant information. You can find it at:
http://www.vr.ucl.ac.uk/depthmap/
The Depthmap manual can be found at:
http://www.vr.ucl.ac.uk/depthmap/handbook.html
There are also four very detailed tutorials that should be studied prior to the use of this
handbook. They can be found at:
http://www.vr.ucl.ac.uk/depthmap/tutorials/
You should also read the following paper by Alasdair about Depthmap:
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Turner, A., 2001, Depthmap: a program to perform visibility graph analysis. In
Proceedings 3rd International Symposium on Space Syntax pp. 31.1–31.9
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Chapter 2 - Axial Analysis
To analyse a configuration in terms of its potential to create movement.
4 Methods for creating the Axial Map
Creating the axial map is of paramount importance as it will be the foundation of your
research. Before reading on, make sure you are familiar with the methods of drawing
the map. A summary of the issues to consider is listed in the next point.
4.1 How to hand-draw an axial map
a. Find an adequate source map over which you can work with precision. This can
be a raster or vector file, but should be appropriate for CAD or GIS use. See the
topic: Drawing in CAD, GIS or Depthmap.
b. Define the area for which you want to create the axial map. Use natural
boundaries (as rivers, highways, rail tracks, etc) whenever possible and be
aware of the edge-effect. Keep your study area well way from the edges of your
axial map by creating a large buffer zone.
c. Draw the longest lines first and evolve to the smaller ones. However, try not to
spread too much around the map to ensure you don’t miss any lines. Complete an
area and evolve from there as possible. try to keep a rational, avoid spreading
unconnected lines all over the map.
Remember, the axial map is the set of longest and fewest lines of sight and access.
It might seem hard and slow at the beginning, but you will quickly get faster.
4.2 Automatically draw the axial map
Depthmap is capable drawing an axial map for you. Through one algorithm, it first
creates an all-line map; through a second algorithm, it reduces the first to the axial map.
To do this, Depthmap needs a base, a layout (from CAD or GIS). This base must be a
polygon (a closed polyline in CAD, or an area feature in GIS).
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The algorithmic definition of the axial map was a significant step for Space Syntax
research, for it cleared up some misunderstandings in regards to the validity of the axial
map. However, in practical terms it has proved less significant for the following
reasons: It needs a purposefully created base; it takes too much computing power and
time to build for large configurations. The potentially interesting all-line map may be
compromised because it depends on the amount of vertices present in the layout which
usually depends on the level of accuracy used as much as on the configuration itself.
Rule of Thumb: Hand draw you axial maps. Use the automatic drawing method for very
specific purposes and on small configurations only. While drawing by hand you will be
getting to know the area and it will, in most occasions, be quicker.
5 Tools for drawing an axial map
In all but exceptional cases, a digital drawing tool will be the best way to draw the map
directly in digital form. There are two main reasons for this:
The laborious and time consuming calculations of the syntactic measures are
only efficiently accomplished by computer algorithms. So you will need your
map in digital format in order to input it to the adequate software, Depthmap.
The quality, abundance and easiness of access to digital data makes it the data
type you are more likely to find upon which to draw your map.
Note: Although the axial map can be hand-drawn in paper (normally in tracing paper
over a reliable source map at an adequate scale that will be around 1:10.000), this is not
a real alternative to drawing it digitally. Even if you were to draw the map in paper, you
would need to scan it, and then digitise it (draw it again in digital format) so it could be
processed by Depthmap. Also, any current computer has the power to run software to
draw an axial map.
5.1 Drawing in CAD, GIS or Depthmap
In terms of the process of drawing the map, the main difference is that GIS uses
projections and CAD doesn’t (with rare exceptions: LandCad from Autodesk for
instance).
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Normally, urban studies need to consider large areas; this implies a cartographic level of
representation (that includes the use of projections) that cannot be achieved with CAD
or Depthmap.
Projections in simple terms: When representing large portions of the naturally curved
earth surface, one must use a projection system. Imagine you want to lay flat a football.
Won’t you need to open it and tear it in order to make it flat? You are deforming the ball.
A projection is just an algorithm that allows us to make this in an organised and
systematic way for the sake of consistency.
The relatively modest dimensions of buildings (in relation to the curvature of the earth)
renders projections unnecessary for their representation. At this scale, a survey of the
terrain is far more relevant than the use of a projection. However, when large distances
are at stake, the lack of a projection may imply a very significant error when it comes to
measure areas, distances and angles.
In addition to this, drawing in GIS usually means creating the map in real coordinates
because the base you use (being also in GIS) will already be georeferenced1. The
advantage of this is that you can at anytime overlay any other georeferenced data to
your map, thus being able to disclose associations of land use for example with
integration values of your map. Most of the available data for planning is georeferenced.
You can also hand draw a map directly in Depthmap. You can import a DXF base and
draw over it. You will after be able to export the data in the same way as if you had
imported the file from CAD or GIS. Just remember that Depthmap do not use
projections, so in this strict sense it is like CAD. Note that, for this reason, automatically
drawn maps will lack projection.
Keep in mind: Any flat representation of a curved surface implies deformation. To
control this we use projections.
Rule of thumb: use CAD or Depthmap for buildings, and GIS for urban analysis.
1 Georeferencing is the process of referencing geographic features to their spatial location. Or in simpler words, to give features on a map their real earth location (normally by the use of coordinates; although other example could be an address). This is very important because by using these universal coordinates we all can display the data accurately and in relation to other data. As an example, when you want to cover a large area with a detailed map you will need several map portions that fit side by side. By using coordinates, each map will be placed in its own spot in relation to other map portions. Or when you are studying a certain area and realize that you need some other layer of information that is in another map of the same area, you can just open it and it will overlay perfectly because it is georeferenced.
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Exceptions: You can, without prejudice, draw an axial map for a small area in CAD (see:
Drawing an Axial Map in CAD and integrating it in a larger map.)
If you want to study a configuration without inserting it in its context (or this context
doesn’t exist) and you don’t wish to overlay other pre-existing data (or data collected by
other people) with your map, the validity of the axial map per se is only in stake when
metric distances and directions (angular analysis) are necessary. Even in these cases,
the errors aren’t usually very significant, although they increase with the size of the
study area.
6 Drawing an Axial Map in CAD and integrating it in a larger map.
Sometimes using CAD makes things easier for you because you are faster with CAD and
because the base you have to work over is in CAD.
If you’re studying the impact of a building or a very small masterplan on the urban
configuration, you can use CAD to draw the axial map and even integrate it in the large
axial map you might have access to in order to analyse the new map in the contextual
configuration. Just carefully follow the next steps:
a. Export the large map (the axial map of the context that contains the area of your
local project) to CAD, open it and identify the area you’re working on. If it’s a big
file you can delete most of it leaving just the surroundings of the area you’re
focusing on (be careful not to erase some long lines that comes close to your
area).
b. Keep all the imported map in one layer.
c. Insert the base to your new map (an image file for instance) or a CAD file.
d. Find your base in the file and move it to place it wherever you want (as
architectural drawings usually use different units than urban ones, you may also
have to scale the base). Never move or scale the whole base-map, just the small
map as this would compromise the coordinates, georeference).
e. Create a layer for the map you are going to draw, and draw it.
f. When you finished drawing your map, export (this layer only) it to GIS and add it
to the whole base-map. Use the same projection system as the whole map in GIS
and your map will be georeferenced (it will have real coordinates in the same
system as the base-map).
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g. Rearrange the recently created lines where necessary. Most likely you will need
to rearrange some of the old ones too to fully transform the two maps in one.
After this you can move to the next step.
h. Export the combined map to Depthmap.
i. Avoiding islands and unconnected lines
j. While drawing, make sure you don’t leave lines unconnected. An isolated line or
a connected set o lines that is disconnected from other set of lines mean that you
will have two graphs, what invalidates the overall results. Isolated lines or sets of
lines are called Islands. Also make sure you delete any rest of line that may be
caused by the design process.
I’ll explain later how you can check for islands once you imported the map to Depthmap.
However, if you find an island at that stage you will have to come back in the process
and fix the problem with the drawing tool.
Because CAD doesn’t use topology (with the exception of LandCad for instance), finding
islands with CAD is not an algorithm task. You cannot ‘ask’ the software to identify the
unconnected lines, or the lines with length < x for instance. Fortunately this is
highlighted by topologic measures, so it can be done algorithmically with Depthmap.
Unfortunately, if you only detect it than, you must come back a step on the process.
Keep in mind: The file (or at least the layer in case you use CAD) you want to analyse
has to contain one single network (see topic 19).
7 The CAD drawing file
The file with the axial map is a normal CAD file, however there are a few aspects that
mustn’t be overlooked:
a. Keep the lines that form the axial map in a dedicated layer. This layer must have
nothing but axial lines.
b. This layer shouldn’t contain any elements but lines. No points, polygons or
polylines.
c. Purge the file before exporting the map.
d. Purge the .dxf file after exporting it, before importing it to Depthmap.
e. Use Western characters only when naming the files. Also make sure that the full
paths to files to be used by Depthmap (or GIS) contain Western characters only.
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8 Multi-scenario assessment - How to add extra value to your map
while keeping it flexible
Sometimes you will want to analyse variations of a configuration. For example you
might want to see the impacts of creating a new line or set of lines, as when assessing
the impact of different proposals for a masterplan (assess different scenarios). Or you
might want to assess different complementary aspects of a network like pedestrian
ways vs. mixed circulation or cycling ways, or highways or private ways. In these cases
you will want to analyse two, three or more variations of a configuration. As an example,
if you’re studying a pedestrian city centre you might want to isolate the pedestrian ways
to study its configuration independently of mixed-use ways. In this case you probably
want to analyse the pedestrian ways only, then the mixed-use only, and then the two
together. So you will be creating three different maps. To do this you need to have the
data structured in a way that allows you to choose what you want to use for each map.
There are two different way to do this depending on the tools you are using.
8.1 Multi-scenario CAD files
When you want ot be able to isloate drawing elements in relation to their attributes you
must first store these somehow. A way to do tihs is CAD is to have the drawing elements
in different layers according to their attributes. So, pedestrian only ways (as in the
example) would be in one layer and mixed-use ways in another layer. When importing
the .dxf file, Depthmap will keep the layer structure and allow you to control which
layers you want to use for each graph. So, you first select them one at a time to produce
the maps of pedestrian-only ways and mixed-use ways, and then select both to create
the map of pedestrian and mixed-use ways together. Just make suer that you don’t
leave isolated elements in any layer (see topic: Validating your Axial Map).
8.2 Multi-scenario GIS files
In the same fashion as with CAD, in this case you should describe the properties of the
lines through attributes. For each map you want to analyse, run a query with the
relevant condition and Export the Selection.
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9 How to export the CAD file with the axial map to Depthmap
If your file contains only the axial map, just purge it and export it to .dxf 2000, .dxf 2004,
or .dxf 2007.
If your file contains other elements:
a. Make sure the axial map is in a dedicated layer.
b. Purge the file.
c. Close all other layers, select all the objects (all the map) and export those to .dxf
2000, .dxf 2004, or .dxf 2007.
d. Use Western characters only when naming the files. Also make sure that the full
paths to files to be used by Depthmap (or GIS) contain Western characters only.
You can always leave other line layers in your .dxf file if you need them in Depthmap.
When imported you can choose what is visible by managing the visibility of the layers.
But note that once you calculate the graph Depthmap will use everything visible, so
make sure your map is isolated in one layer. Also, the larger the file you import to
Depthmap, the more easy it becomes to include in the map something you don’t want to
and the larger the file the heavier to work with.
10 How to export the GIS file with the axial map to Depthmap
Depthmap reads some GIS files directly (see updates in Depthmap manual). So there is
no need to export. If Depthmap dos not read the file type your data is in, you will need to
convert it. A suggestion is to use Universal Translator. This is a part of the GIS software
MapInfo. The advantage with this is that Depthmap reads MapInfo native format, .MIF
and .MID. So this translator will be able to transform nearly any format to the format
read by Depthmap.
Note: Use Western characters only when naming the files. Also make sure that the full
paths to files to be used by Depthmap (or GIS) contain Western characters only.
11 Converting ‘any’ GIS file type to Depthmap’s GIS file format MIF
In MapInfo go to TOOLS - UNIVERSAL TRANSLATOR. You don’t have to start a session, a
blank file will give you access to what you need.
a. Choose the format your file is in, then choose your file.
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b. Choose the format .MIF as destination format.
c. Choose a destination folder.
d. Depending on the size of the file, this can take from a few seconds up to a few
hours.
12 Unlinks
For the sake of the easiness of the process, and acknowledging the planar nature of the
vast majority of street networks, an axial map is interpreted by the software’s as a
planar graph. This means that there is a node on every intersection of the edges of the
graph (the edges of the graph are the axial lines). However, urban systems do have
exceptions to this, such as viaducts or tunnels. This way, when you draw the axial map
and represent a viaduct for instance, you will represent it in the same plane as the rest
of the city. As a consequence, the software that does a great job with the vast majority of
lines by interpreting crossing lines as actually directly linked to each other by a node, is
induced in error in these exceptional circumstances. In such cases, we must override the
software and ‘make it notice’ that although certain lines cross, they do not form a node.
Due to its unlinking nature, these cases are called unlinks.
12.1 How to use unlinks
There are two options to deal with unlinks: manual, where you identify each case one by
one in Depthmap; and automatically, by creating a point file in CAD or GIS with the exact
location of the point where the lines cross but don’t form a node.
12.2 Manual vs. Automatic Unlinking
If there are just a little amount of unlinks and you can identify them easily in the axial
map, you will be tempted to do it manually, and you are right, in that it takes less time.
However, if for larger amount of unlinks it is strongly recommended that you create a
file with the unlinks, it might sometimes be better to do so even for smaller quantities.
Note that the most significant advantage of creating a file is that by doing so you will be
creating a file with information that can be passed on to other users. If you or someone
else needs to re-use the map later on , the data will be ready to be used. This is
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extremely useful when a few years later you want to update your map. The unlinks file
is there ready to be updated too, but you won’t be forgetting any unlink. The best way to
work in the vast majority of cases is to create an unlinks file to always go along with the
axial map even when there are few unlinks.
To decide if you should create the file or not, consider how much work you invested on
the map and if this single use is the most you can get from it.
12.3 How to create a file with the unlinks of your axial map
Either you are working in CAD or GIS, just create points rigorously in the locations
where crossing axial lines do not create a node. Be precise with this because this point
store the exact coordinates of these events. Although Depthmap has a small tolerance
for this, it is so easy to draw this points with correct coordinates that there is no point in
not doing it. Also, be careful as this is very tricky, especially when drawing in CAD,
because you can hardly see the points. So you may lose track and end up missing some
and/or creating duplicates. A way to avoid this when you have many unlinks is to create
circles (use a distinct colour and line weight). Draw them around the unlinks to mark
them as ready. Remember to keep the circles in a separate layer. Do not insert symbols
as blocks or circles or crossing lines to mark these locations instead of points. You must
use points, and keep them in a dedicated layer.
12.4 How to export the unlinks file from CAD
The best option is to export the unlinks to DXF (or just save as DXF if your CAD package
is Autocad) and then use the Universal Translator from Mapinfo to convert your DXF to
MIF/MID (in Mapinfo, go to TOOLS, UNIVERSAL TRANSLATOR, then follow the as
explained in the next point (The MIF file).
In previous versions of Depthmap, this would have been the solution (this is mentioned
only as an alternative, in case you experiment problems with the one presented above):
You want to export a list of the pairs of coordinates. This list will be in a text file (.txt).
CAD software can normally export this as an ASCII file (depending on your software and
version, you might need to find an app online to do this, there are free ones). An ASCII
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file is a file that contains binary information in a format that is easy to understand for
humans. In this case it will look like a list when opened with a simple word processor
like Textedit (Mac OS) or Notepad (Windows) as shown in figure 1.
Note: Do not open TXT files with advanced word processors like Microsoft Word or
Pages.
12.5 How to export the unlinks file from GIS
The unlinks will be a point feature theme. Just export it as MIF/MID, or in another file
type and then convert it to MIF/MID. It will be ready to import to Depthmap.
If you need to export as TXT:
a. Create two fields for attributes to store the coordinates of the points, name them
“X” and “Y”.
b. Fill in these fields with the coordinates of each point feature. This is done
algorithmically by the GIS software.
c. Export this table as MIF/MID (or in any other file type and then convert it to this
through Universal Translator tool from MapInfo).
13 Links
Like unlinks, Links are exceptions to the drawn map. For instance, when you work with
a multi-floor building you will represent the floors side by side. The axial map of each
floor will then be isolated from the other floors. In order to correct this, links must be
manually established between the vertical accesses as elevators, stairs or ramps.
13.1 How to create a link
Figure 1- The format of the TXT file is as shown.
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a. Select one of the lines you want to link (this line will be highlighted as selected).
b. Choose JOIN form the top menu, than right-click on the element on the other
floor that you want to link the previous line to.
c. The link should have been done.
d. Check that the link has been done by pausing the cursor over one of the lines you
linked and check the new value of connectivity (remember that to see
connectivity values you must chose connectivity from the vertical left pane).
14 How to import the CAD file(s) into Depthmap and convert your
map into a graph
Depthmap reads DXF files, which your CAD package will be able to export to, or save in.
The export process has been explained in a previous section.
You can draw the axial map in CAD and import it, or you can load a base and draw your
axial map in Depthmap. See topic: Drawing the axial map in CAD, GIS or Depthmap.
Remember; you have to create a new graph before importing data to Depthmap (if you
still didn’t do so. To do this go to FILE, NEW).
To import: Go to top menu LAYER, IMPORT, choose the adequate file type and then your
file.
Whatever is that you import, even if it is an axial map ready to be used (or eventually
used before), Depthmap will treat it as a base only. You will have to convert it to axial
map. Go to LAYER, CONVERT DRAWING LAYERS... and choose axial map. You can also
name this new layer map that Depthmap is creating.
Now is the time to deal with unlinks (or links).
Only now your map is ready for the syntactic measures to be calculated.
Go to TOOLS, POINT/AXIAL/CONVEX, and choose RUN GRAPH ANALYSIS.
15 How to import the GIS file(s) into Depthmap and convert your map
into a graph
The only GIS format that Depthmap can import is MIF. You will be familiar with
MIF/MID files if you work with MapInfo, for these are the file type pairs that this
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package uses to import or export data. If you worked with another package either
export the map (and/or unlinks file, separately) in MIF/MID, or use other file type and
convert your file to MIF/MID. To do this conversion use MapInfo Universal Translator
tool. In Mapinfo go to TOOLS, UNIVERSAL TRANSLATOR, and convert your file to
MIF/MID.
Once you have you MIF/MIF pair of files you are ready to import them to Depthmap.
Remember; you have to create a new graph first (if you still didn’t do so. To do this go to
FILE, NEW).
To import go to LAYER, IMPORT, choose the MIF file type, then your file.
Your file has now been imported, but it will be treated as a base only.
Now you will have to transform it in an axial map (even if you are re-loading a MIF/MID
file that you have already calculated with Depthmap in the past. In this case your old
measures will be available on this base, but to calculate the map again you must first
convert that layer to an axial map.)
Go to LAYER, CONVERT DISPLAYED LAYER..., and convert it to an Axial Map. At this
moment Depthmap is creating the graph over which it will calculate the syntactic
measures, so remember to update it with Links and/or Unlinks before you run it.
Please read ahead for an explanation as why GIS data are divided in multiple
complementary files, and the practical implications of this: GIS File Types.
16 GIS File Types - Why multi-files and its practical consequences.
One thing you will notice about GIS files is that they are always in pairs (at the very
least).
You may normally associate a computer file with the data you have input on it; so for
instance in a word processing file you have the words that you typed. However, this file
contains much more than that, it also contains all the formatting, and metadata (this is
data about the file, as when created, last time edited, file type, etc). A file has much more
than just the data itself, it also contains information about the data and about the file
itself.
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GIS files contain even more, they contain the graphic data, one or several tables with
attribute data associated with the graphical features, it contains projection systems,
metadata, etc. Because these files have so much data, GIS packages typically divide it in
complementary files. So while your CAD drawing or Word report would be all in one
self-sufficient single file (e.g. plan.dwg, or report.doc), a GIS file will have at least two
parts, for instance plan.mif and plan.mid. When you load your files (in Depthmap for
instance) you will apparently only load the MIF one, however, the computer is
recognising the pair, and will not be able to load it if only one is found. When
working with GIS files always be careful as to move or copy all the complementary files
together, as one only won’t be readable. The files must always be together, in the
same folder. Complementary files are easy to identify because they have the exact same
name with a different file extension, for instance, masterplan.mif and masterplan.mid.
17 How and when to import unlinks file to Depthmap
Whatever map you import to Depthmap, it will be considered as a base only. In order to
calculate the syntactic measures, Depthmap needs a graph. So the first step is:
Create a graph based on your layer(s). To do this, you must select, from the layers that
you imported, the layer (or combination of layers) that you want to analyse. Then go to
LAYER, CONVERT DISPLAYED LAYER..., choose AXIAL MAP from NEW LAYER TYPE, and
name your new map.
It is at this moment, when the graph has been created, that you must deal with
possible links or unlinks. Check Depthmap manual for the manual option.
If you have an unlinks file, this is the moment to use it.
Import your unlinks file as described below, depending on your file type.
Tip: Always check that this has worked by positioning the cursor over an unlinked line
(remember to choose connectivity from the left menu).
17.1 Importing the unlinks DXF file from CAD
The more straightforward way of doing this with the current version of Depthmap is to
use Universal Translator from Mapinfo (TOOLS, UNIVERSAL TRANSLATOR) to convert
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you DXF file to MIF/MID, and then to import it to Depthmap. Then follow the procedure
discribed below under the topic: Importing the unlinks MIF/MID file from GIS.
17.2 Importing the unlinks TXT file from CAD
Having created the unlinks file as previously described, once you have your drawing
loaded in Depthmap and converted it to axial map, go to TOOLS,
POINT/AXIAL/CONVEX, LOAD UNLINKS FROM FILE. The software will import your file
and use the unlinks in the selected axial map. Only after this you’ll be ready to run
calculations in Depthmap.
17.3 Importing the unlinks MIF/MID file from GIS
You will import the MIF file to Depthmap and then convert the point features to unlinks
by using TOOLS, POINT/AXIAL/CONVEX, CONVERT DATA MAP POINTS TO UNLINKS.
This feature is fairly recent (and very useful), for the old and more laborious alternative
see next point (it might be useful just in case you experiment difficulties with the
previous alternative).
An older and less practical alternative would be to Open the .dbf file (that results from
the export) in excel and save it as .txt. Your unlinks file is ready to be used in Depthmap.
It should look as shown in Figure 1.
18 Analysing the Axial map
18.1 How to calculate the syntactic measures of your map
Once you imported your map, chose the layer(s) to create a graph, once you have
created the graph, and linked and/or unlinked specific nodes, your graph will be ready
to the analysis. This is described in detail in the Depthmap manual and will be shortly
dealt with here.
Go to TOOLS, POINT/AXIAL/CONVEX, choose RUN GRAPH ANALYSIS.
Chose the appropriate settings and run the analysis. This may take from a few seconds
to a few days depending on the sizeof your graph, and the settings used.
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18.2 How to control which measure is displayed
Once you run the analysis on the graph (in other words, calculated the syntactic
measures) you can choose from the left pane which measure you want to see displayed
on your map.
18.3 How to display the table where the values of the syntactic
measures are stored
Use the menu WINDOW, and choose TABLE.
18.4 How to display several views of the data simultaneously
Keep in mind that wether you open the map, the table, or the scatter plot, you are seeing
the same data; although from a different perspective. Each view allows you to
appreciate different properties of it. So, if you’re looking for spatial patterns you will
want to see the features mapped, but if you want to analyse relational patterns you may
prefer to look at it through a scatter plot, and if you’re looking for patterns of values you
may prefer the table view.
In addition, it is sometimes extremely useful to be able to see the data in different views
simultaneously. For instance, you may want to see the values in the table associated
with a line that you select on the map, and/or where it falls in a correlation. When
working with axial maps, Depthmap allows you to have any combination of up to 3
simultaneous views.
Just open the views you want from the WINDOW menu, and choose up to three, from
MAP, SCATTER PLOT and TABLE.
Then, again in the menu WINDOW, choose TILE.
All the selected views should now be simultaneously visible. Plus (and this is a big plus)
whatever elements you select in one view, will be showed as selected in all other views.
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19 Before analysing the data - Validate your axial map
It has been previously mentioned that the presence of unconnected lines or islands
jeopardises the analysis. These must be deleted or connected to the rest of the map and
a new graph has to be built and analysed. So, before using the data, it is worth checking
if Depthmap found a non-reported error.
19.1 Detecting unconnected lines
Two different types of error can be found: isolated lines and islands, each requiring its
own investigation method.
19.2 How to identify isolated lines
You always want to detect these as early as possible, so it is good practice to check for
isolated lines even before you run the analysis. This is possible because, when creating
the graph, Depthmap creates a few values, one of which is topological - Connectivity.
This basic syntactic measure indicates the number of lines each line is directly
connected to. So an isolated line will have zero connectivity.
From the moment you create the graph, you can open the table with the values and click
on the name of the column ‘Connectivity’ to sort lines by its connectivity values. If there
are any zeros they will show in the first lines, and this means that there are
unconnected lines. To identify these on the map, select them on the left of the “Ref
Number” column, and the unconnected line(s) will show as selected on the map. You
will this way know what to correct in you map.
19.3 How to identify an island
An Island is a set of lines connected between them, but isolated from the rest of the map.
These are more difficult to detect because the lines themselves aren’t isolated (so they
will have connectivity) and only after running the analysis they become identifiable.
The first thing to notice is the presence of negative integration values. There won’t be
any in one system, so their presence reflects the existence of an island.
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But depending on the system, especially with smaller ones, you might not get negative
values at all. In this case, an alternative is to have a look at depth based values. This is
because most commonly only a small portion of the map is disconnected. This means
that Depthmap is analysing two systems of different sizes, what will be clearly
expressed by their depths.
How to identify islands based on depth:
With both the table and map visible (WINDOW, TILE), click on the table to re-order the
column Mean Depth (also choose Mean Depth as the displayed measure on the map).
Scroll through the values and you will probably find a significant discrepancy in them.
This is because one systems is much larger (in terms of the number of elements) than
the other. If you calculated Total Depth, this will be particularly noticeable because you
will have differences of possibly several orders of magnitude (10x) between values.
20 How to export image files of maps created in Depthmap
a. Prepare the map by choosing the measure you want to display.
b. Adjust the area with pan and zoom.
c. From the menu EDIT choose EXPORT SCREEN.
d. Name the image you’re creating (don’t forget to mention the syntactic measure it
reports) and choose a folder to save it to.
e. The image will be an EPS file type, which is a vector format for higher displaying
and printing quality, and is ready to be imported to presentations or reports.
Tip: When preparing several images of the same area, it is worth first choosing the
adequate zoom and adjust the visible portion of the map before exporting the set of
images. If you then don’t re-adjust these, all the images will display the map in the exact
same position. This is very important as it helps the audience to read the maps.
21 How to correlate different variables - Scatter Plots
Depthmap can produce scatter plots, which allow you to explore correlations between
syntactic measures (or other data that you might have loaded, as observations) from
your dataset. These proceedings are carefuly described on the Depthmap tutorials , so
they will be mentioned lightly here. I’ll just highlight a few points worth noticing.
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21.1 To produce a Scatter Plot
Go to menu WINDOW, and choose SCATTER PLOT.
A window will open with a default scatter plot. This default uses the measure of that is
displayed at the moment in both axis.
Choose the measures you want to correlate through the drop-down menus on the top of
the window.
You can add information to this scatter plot:
The R2 value.
The trend line.
The equation of the trend line.
Note and Tips: Note that, while a scatter plot implies the presence of two measures, the
elements are still displayed in colour. So, in which measure is this colour scale based
on? It is based on the one chosen on the vertical left pane; it is independent from the
measures represented on the scatter plot. This allows for an introduction on the image
of the scatter plot of yet another variable. You may or not want this. To turn it off, you
can use the button TOGGLE COLOUR on the top of the scatter plot window, which
colours all elements in white. This is a very useful feature because it also allows you to
clearly identify a selection of features (which will be coloured in red).
21.2 Correlation of a selection of elements
Depthmap does not allow you to do this. You will have to export your data and complete
your analysis in a statistics or GIS package. However, Depthmap will display selected
data in all views. This way you can see where the element(s) you select fall in the scatter
plot in relation to all others, and to the trend line. This is very useful when analysing the
Intelligibility of a particular element or part of a configuration. Although you won’t have
a R2 value for your selection, you can see if that is worth exploring further, and if that is
the case, export the data to analyse in more detail.
21.3 How to export image files of Scatter Plots created in Depthmap
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Prepare the Scatter Plot by choosing the measures you want to correlate and add the
additional information (as the R2 value for instance). Remember you can also eliminate
the colour scale and include a selection of elements.
Make sure you have the scatter plot window active. From the menu EDIT choose COPY
SCREEN.
An image file of your scatter plot has been copied to the clipboard, but it is not saved on
a folder as when you Export Screen. You must insert this image immediately in your
document by PASTING it. Or you can edit it with an image editing package like
Photoshop, again by pasting it on a new image file.
22 How to export the syntactic measures to EXCEL, SPSS, JMP or GIS
Depthmap is a very specific research tool dedicated to the exploration of configurations.
Logically it lacks depth on other fronts, as statistical analysis, other spatial analysis and
data management.
You will often want to explore your data further. If you simply want to use more
sophisticated statistical analysis you can export the table associated with the map and
use it with a statistical package as SPSS or JMP. If you are more familiar with Excel you
can also use it, depending on if it does what you require. However, Excel is often useful
as a transition for the exported data (please read ahead about exporting data for
statistical purposes).
The main issue to consider though is that by doing this you will loose the link between
the attributes on the table (the syntactic measures) and the lines on the map. This is
often undesirable. Depthmap actually exports the pairs of coordinates of the lines, but in
a statistical package they won’t be of much use. Only a GIS package would be able to
“redraw” the map and keep the attributes of each line.
However, if you want to keep the attribute data (the table) and the (geo)graphical
features (axial lines), you can export your data directly in a GIS format. This has three
extra advantages: It allows the overlay of other layers of georeferenced data as
infrastructure, social and economic data, administrative boundaries, etc; GIS packages
normally have a good set of tools for spatial analysis and data management; and a
comprehensive set of statistical tools too.
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22.1 How to export data for statistical analysis only
As explained before, in this case you will only be exporting the table with the values for
each syntactic measure, but you will be leaving behind the axial lines to which they are
associated to.
Go to menu LAYER, EXPORT, choose a folder to place the file to export, name it and
choose SAVE AS TYPE: TXT .
Having exported the TXT file (which is tab delimited, meaning that columns of values
are separated by a tab space) that is compatible with most statistical packages. In case
you experience any difficulties, first open it in Excel, save it as XLS (not XLSX) (or DBF4
file with Excel versions prior to Office 2007) and open it with your statistical software.
22.2 How to export data to GIS
As previously explained, exporting to GIS will keep all your table values and your map,
as well as the associations between them.
Go to menu LAYER, EXPORT, choose a folder to place the file to export, name it and
choose SAVE AS TYPE: MIF .
If you navigate to the folder where your file has been saved you will notice that in fact
two files have been created: filename.mif and filename.mid. These files are
complementary and will not work if separated. You must always keep them together, in
the same folder.
If your GIS package reads MIF/MID files your data is ready to be used.
If your GIS packages dos not read MIF/MID files, use the Universal Translator tool from
MapInfo to convert the pair of files to a convenient file type. In Mapinfo go to menu
TOOLS, UNIVERSAL TRANSLATOR, and choose the file and adequate file types.
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Chapter 2 - Segment Analysis
23 Segment map
23.1 From axial map to segment map (why always make axial map
first)
The segment map is always created by Depthmap from the axial map. Links and unlinks
must be defined in the axial map so they are then carried on to the segment map.
Note: Linking and unlinking operations cannot be carried out on the segment map.
23.2 Using an axial map to create a segment map
Create the axial map as prveviously described, then do the necessary (un)linking and
only after from the top menu go to LAYER, CONVERT DISPLAYED LAYER (make sure
you only have your axial map visible) and convert it to segment map.
23.2.1 Dealing with Stubs
When drawing axial maps we typically intersect axial lines instead of making them stop
when they reach another line. This is sometimes necessary as the lines eventually
continue to another space. However, it is often the case that these extentions of lines do
not in fact serve to access another space. These segments of axial lines that are
unecessary are called stubs. Leaving stubs in the graph would create artificial
connectivity (both traditional (number of connections), and angular).. Stubs should
therefore be removed whenever possible. Depthmap allows you to remove stubs by
defining a treshould from which it deletes them. This is defined in terms of the
percentage of the initial line lenght. Defining this parameter should be done cautiously.
Depending on the dimension and diversity of the street layout, you might want to carry
out afew trials to find the best ratio (in the form of percentage) for each particular case.
As a rough guide, this shall normally be around 20 to 40%.
23.2.2 Analysing the segment map
34
From top menu TOOLS, SEGMENT, choose RUN SEGMENT ANALYSIS.
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Chapter 3 - Visibility Graph Analysis
24 Visibility Graph (the ‘map’ to perform visibility analysis)
24.1 How to prepare CAD files to VGA
The first thing to consider when it comes to create a base plan over which to run
visibility analysis is that the plan must be organised in terms of occluding elements. In
other words, the drawing file must be organised in layers in a way that, at the time of
analysis, one can only have on the layers that contain the occluding edges one want to
be considered. As an example, if a wall is normally an occluding edge, and so makes
sense to have it on a layer that is turned on when the analysis is carried out, you may
not wan tot consider a low wall (50cm high for instance). In this case you must keep this
wall in another layer, so you can turn it off before running the analysis. Always keep in
mind your objectives. If you are analysing a nursery for instance, you might want to
include the lower walls (mentioned in the previous example) and even some furniture
that is occluding for one of the types of user. In this case you might want to run two
analysis, one for the visibility of adults and one for that of children.
Note that you should sometimes consider furniture, but then, most likely not all in the
same way. For instance large tall cabinets are different from desks or chairs when it
comes to their impact on visibility.
Depthmap also allows you to correct a situation before you create the graph. You can
add a line as if separating spaces (for instance if you want to simulate a closed door, or if
a wall is missing). However it is good practice to carry out all the changes in the CAD
file. The pencil feature is on the top of the display window, just select it to use it.
A second fundamental issue is the boundary. The area of your plan that you want to
analyse must be a polygon. You don’t need to explicitly draw a polygon in CAD,
Depthmap will recognise the limits of the area that you will indicate as the one to
analyse. In order for Depthmap to be able to recognise this, your drawing must be
accurate in a topological ‘object snapping’ sense (this means lines must really join, pay
36
special attention to ‘T’ junctions. Also, if the area to analyse is not delimited, you must
artificially create the boundaries. In these circumstances, make sure you create these
well away from your study area (in graph terms). In some cases you can use CONTEXT
FILLING. This is an important feature that allows you to treat peripheral (contextual)
areas with a different (lighter) resolution. This feature is available from the top of the
display window on the icon FILLING (looks like a bucket). Do not click on it. Choose the
dropdown menu and choose CONTEXT FILL rather the default Standard Fill. Now select
the contextual area. This can save you a significant amount of computation time.
One other detail to pay attention to is the orientation of your plan in the file. In order to
analyse you plan, Depthmap will create a grid over it. This will be explained in the next
sections, but for now you must know that the grid aligned to the Cartesian axes XY. As a
consequence, you should consider aligning your layout withh the XY reference system.
(Somehow, within your CAD file, keep track of this change for future reference).
Aligning the axis of the layout you want to analyse with XY will increase the quality of
the presentation of your analysis.
Keep in mind
a) Always keep your drawings organised and flexible. Remember that the central
feature is visibility, so the drawings must be organised in terms of occluding
edges. This way you will also be able to explore different scenarios, for instance
analyse a floor with open and closed, say doors and/or windows. You can also
use this flexibility to analyse different layout solutions (for instance for different
users or circumstances).
b) You must provide a boundary.
c) Consider rotating the plan to align it to XY Cartesian axes.
24.2 How to prepare GIS files to VGA
When using GIS data follow the same rational suggested to the use of CAD files.
24.3 How to export CAD files to VGA
37
In a similar manner to exporting an axial map, just save it as DXF and open it in
Depthmap.
24.4 How to import CAD files to VGA in Depthmap
In a similar manner to importing an axial map. just import it to Depthmap. You will be
able to control which layers to have visible to run the analysis, Mind that you can always
make layers visible after the analysis if you wish to export an image for instance. This is
done to make a plan more comprehensible to an audience, for instance. When doing this
though, make sure you mention that those objects (those from the layer later included)
were not considered in the analysis.
24.5 Running the visibility graph analysis
Before analysing a plan, make sure you control the layers according to the needs of your
analysis in particular.
In order to run the analysis you first need to identify which is the area(s) to analyse.
Depthmap helps you doing this by recognising the limits of the area indicated by you.
Do this by selecting the bucke-like icon from the top of the display window, then click
inside the area to analyse.
At this moment, Depthmap will create a graph of the area to analyse. It creates a square
grid of points from which it will then create the visibility graph. This grid is
automatically extended throughout the study area chosen to analyse. Naturally, the
links of the visibility graph are defined by relations of visibility between the points in
the grid, considering the layout. When creating the graph, some basic measures, as
connectivity, become available, but the analysis hasn’t been done yet. To run the
analysis go to TOOLS, VISIBILITY, RUN VISIBILITY GRAPH ANALYSIS.
24.5.1 Setting the grid
The first thing to know about the displayed grid is that it is an artificial resource to help
us work, much like a visual aid. The actual points considered by the software are
invisibly set in the centre of the visible squares. However, in order to actually show
38
these, they have been given area; the size of the square grid. This explains why
sometimes the grid appears to lay over obstacles. It happens because while the point
itself is kept in the open space, the visible grid may actually overlay the obstacle.
When setting the grid, a normal question is: which grid spacing to use. This is relevant
for two reasons: First, the size of the grid (the spacing between points) represents the
definition of the analysis; second, the size of the graph grows exponentially with the
number of nodes it contains2. This shows the need for a balance between an analysis
that is precise enough for the aims of the study, but which does not compromise the
resources of computation power, and time. Although a sense for balance is achieved
through experience, similar results can be achieved by carrying out experiments.
Running several experimental analysis usually ends up saving you time and helps
guiding the orientation of your analysis. Start by using large grids and reduce the
spacing gradually as it becomes necessary. Always keep your goals in mind and adjust
the spacing to them. Different grid spacing will, in principle, be required to analyse a
building plan or an urban square, or an urban neighbourhood.
Depthmap suggests a default value for the grid based on the dimensions of your
drawing. This is a reference value that can be changed depending on the aims of your
analysis.
Considering that Depthmap creates a square grid oriented along XY Cartesian axes, it is
sometimes a good idea to rotate the plan in CAD (before exporting it) in order to align
its longest axis with X and Y.
Note that although a tighter grid means a higher density of spatial units and therefore is
likely to produce less ‘pixeled’ images, your main goal is to satisfy the needs of your
analysis.
24.6 Isovists
Depthmap does not create isovists. As a graph analysis tool, Depthmap does not directly
analyse geometry. However, through the calculation of Step Depth, one can simulate an
isovist.
2 The number of nodes from a graph is called its degree.
39
a. Once you have created the visibility graph, chose a point (or set of points
by selecting a rectangle with the mouse);
b. In the top menu TOOLS, VISIBILITY, chose STEP DEPTH, VISIBILITY STEP.
Depthmap creates a new table with the depth values from the selected point(s). Step
depth 1 values are showed in red, these are the isovist. Other step depth values are
displayed in other colours.
Note: Although the first time you run the Step-depth tool a new set of data is created as
a field on the table and a layer in the left pane, all the next times you run it this data will
be updated and you lose the previous one. In case you want to keep these analysis you
must rename it before running the next one (do this by right clicking on it). Now when
you run the analysis your data will not be overwritten, instead a new field will be added
with the original name ‘Visual Step Depth’.
24.7 Boundary Graph
This analysis aims at highlighting the edge of the graph (the boundary of the free space,
typically along walls), by showing values of the edge as visibility target. This is
particularly useful when you are trying to identify which of the boundary areas are most
visible from within the space. May be you’re looking for a place where to put a sign, for
instance.
24.8 About the grid and the graph
Once the grid is made the graph is created. This cannot be undone. Although it is not
fully calculated, the number and location of points is defined and the links (relationships
of visibility between them) are established. Although not analysed, the graph is
complete. This cannot be undone or changed.
It is good practice to save the file once all the data (layouts) are loaded and ready to be
used. Keep this version unaltered and save another one where you will actually make
the graph and run analysis. This way you can come back to the original version again
and again effortlessly until you’re happy with the result.
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24.9 Context filling
This has been created to save you processing time when you want to include a certain
area on the analysis that is not the area that you are studying. In other words, when you
want to give visibility context to the area you want to study.
The same way you fill the study area with the tool that ‘floods’ the free space, you
choose Context Filling and ‘flood’ the context area.Depthmap will treat this contextual
area in a different way. Not when creating the graph, but when analysing it, Depthmap
will ignore a substantial proportion of context points which leads to a substantial
reduction of processing time without compromising the accuracy of the results.
When using context filling, make sure you select the grid size in a way that at least two
points of the grid fit into narrow spaces and passages that you wish to include in the
analysis. To make sure that Depthmap is getting wherever you want to include on the
analysis, you can use step depth to make sure all areas are covered.
When using context filling there might be some apparent behaviour when it comes to
use the selection control, see (Turner 2004; page 18).
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Chapter 4 - Convex analysis
To analyse a configuration in terms of its static relationships.
25 Convex Space
Spatial convexity is used to define the potential for interaction in person. A convex
space is defined as a spatial unit from where any two points are visible.
In geometrical terms, a convex space is defined as a polygon where all possible pairs of
points may be connected by a straight line without this crossing its boundaries.
26 Convex map
The least set of the fattest convex spaces necessary to fully cover a layout, and the links
between them.
27 Tools to draw the convex map
27.1 Drawing the convex map in Depthmap
You can easily draw the convex map directly in Depthmap. You can import a DXF file for
example to work as base. Then:
a) Create a new layer
b) Draw the polygons. You may want to create a grid (as for VGA) just to snap to
when drawing, and then delete it. To snap to, hold CTRL when clicking. Do not
double click. To close the polygon click back on the initial point.
c) Link the polygons by using the LINK button on the middle-top of the drawing
window.
d) Make sure all spaces are linked. There must be no isolated spaces.
e) While creating the links you can select connectivity from the left window pane
and you will see the connectivity values being updated as you progress.
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27.2 Drawing the convex map in CAD (or GIS)
If you have drawn you convex map outside Depthmap, you can still use it. Import it to
Depthmap and convert it in convex map by using the top menu LAYER. You then have to
draw the links in Depthmap as described in the previous point.
27.2.1 The drawing file in CAD
If you draw your map outside Depthmap make sure you have a clean file, or layer. All
polygons must be closed polylines. Isolate you convex spaces in a layer and create a DXF
file with the polygons only. Purging the file may save you future complications.
27.2.2 The drawing file from GIS
Most likely, if in GIS, your file is ready to be used. See the considerations about
preparing a CAD file.
28 Running Convex Analysis
In the same way you run axial analysis. From top menu TOOLS, choose
POINT/AXIAL/CONVEX and RUN GRAPH ANALYSIS.
You can also run Step depth analysis on convex maps. Proceed in similar fashion as with
axial and VGA Step Depth (see topic 24.6).
References
Turner, Alasdair; Depthmap 4; University College London, 2004
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