gis - - the best way to create ugly maps fast. more bad maps…
TRANSCRIPT
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GIS - - the best way
to create ugly maps
FAST
GIS - - the best way
to create ugly maps
FAST
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More bad maps…
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Representing and Transforming
• Graphic symbols• size, symbology, value, saturation, shape, arrangement,
texture, focus
• Classification procedures are used to ease user interpretation • Natural, quantile, equal interval, s.d.
• Cartogram transformations distort area or distance for some specific reason
More examples: US Transportation Survey
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Components of Geographic InformationComponents of Geographic Information
Geographic InformationGeographic Information
ThemeTheme TimeTime SpaceSpace
NominalNominal
OrdinalOrdinal
IntervalInterval
RatioRatio
PointsPoints LinesLines AreasAreas VolumesVolumes
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(A Start at) a Typology of Thematic Maps(A Start at) a Typology of Thematic Maps
fixed controlled measured
geological time theme location
map
census data time location theme
weather location time theme
report
tide table theme location time
flood hydro. location time theme
grid cell data time location theme
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Vector and Raster - two main families Representation of geographic information:
– Raster: location controlled, attribute measured values are stored in ordered array, so that position in the array defines geographic
location
– Vector: attribute controlled, location measured geographic coordinates are stored separately from attributes, connected with Identifiers
Geographic Data ModelsGeographic Data Models
V
(v1,v2)3 43 12 3 45
15 40 2 15 24
21 3 5 10 64
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Rasters• How to represent phenomena conceived as fields or
discrete objects?• Raster
• Divide the world into square cells• Register the corners to the Earth• Represent discrete objects as collections of one or more cells• Represent fields by assigning attribute values to cells• More commonly used to represent fields than discrete objects
• Characteristics:• Pixel size
• The size of the cell or picture element, defining the level of spatial detail• All variation within pixels is lost
• Assignment scheme• The value of a cell may be an average over the cell, or a total within the
cell, or max, or min, or the commonest value in the cell, or presence/absence, or…
• It may also be the value found at the cell’s central point, or systematic analigned
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Legend
Mixed conifer
Douglas fir
Oak savannah
Grassland
Raster representation. Each color represents a different value of a nominal-
scale field denoting land cover class.
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The mixed pixel problem
W GW
W W G
W W G
W GG
W W G
W G G
W GE
W E G
E E G
Water dominates Winner takes all Edges separate
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RASTERS…
• Each cell can be owned by only one feature.• Rasters are easy to understand, easy to read and
write, and easy to draw on the screen. A grid or raster maps directly onto an array.
• Grids are poor at representing points, lines and areas, but good at surfaces.
• Grids are a natural representation for scanned or remotely sensed data.
• Grids suffer from the mixed pixel problem.• Grid compression techniques used in GIS are run-
length encoding and quad trees.
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Rasters and vectors can be flat files … if they are simple
Vector-based line
Raster-based line
4753456 6234124753436 6234244753462 6234784753432 6234824753405 6234294753401 6235084753462 6235554753398 623634
00000000000000000001100000100000101010000101000011001000010100000000100010001000000010001000010000010001000000100010000100000001011100100000000100001110000000000000000000000000
Flat File
Flat File
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Compacting RasterCompacting Raster
from simple matrix to...
...run-length encoding
...row differences encoding, TIFF
...Quadtrees, Morton numbers
10
3203
1
21
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Vector - Land Records
GIS
Survey
9/
/
/ / /
/
30.5’ 26.23’
20.37’ 26.23’
45.8
1’
45.8
1’
35.4
4’
R 10’
12 13
Survey point
Computation
Link
Surveyed feature
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Vector Data Structure Alternatives 1Vector Data Structure Alternatives 1 Development trends:
– increasing complexity, refining logic– making geographic relationships EXPLICIT
Spaghetti files (1974...)– the original CIA format– lines and points which the
reader must organize
Polygon loops (location lists):– polygons stored as objects, polygon
shading is easy, IF CORRECT!– problems: common line defined twice;
slivers between adjacent polygons because boundaries not necessarily the same
(x1,y1)
(x2,y2)(x3,y3)
(x4,y4)
(x5,y5)(x6,y6)
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Point dictionary– polygon descriptions refer to lists of fixed
points with coordinates (point dictionaries)
– similar to polygon loops, but instead of coordinates of vertices in polygon descriptions - IDs of vertices
Topological data structure– Organizes Points, Lines, and Areas as
Nodes, Chains, and Polygons– The model: nodes bound chains, chains co-bound polygons;
chains co-bound nodes, polygons co-bound chains...
– the structure stores topological relationships between nodes, chains, and polygons; these relationships are used in defining chains through nodes, polygons through chains, etc.
– Provides for contiguity, better quality control...
Vector Data Structure Alternatives 2Vector Data Structure Alternatives 2
1
23
4
5
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TopologyTopology
TOPOLOGY: study of basic spatial relationships based on intuitive notions of space (those not requiring numerical measurements); fundamental level of mathematics of space;
Topology IS NOT topography– TOPOGRAPHY: measurement/representation of earth
elevation and related features (a form of general/ reference map)
Why topology in cartography/GIS– lines are coded once - avoids redundancy– data quality issue: [topo]-logical consistency
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Basic arc topology
n1
n2
123 A
B
Arc From To PL PR n1x n1y n2x n2y1 n1 n2 A B x y x y
Topological Arcs File
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Arc/node map data structure with files
1 1,2,3,4,5,6,7
Arcs File
POLYGON “A”
A: 1,2, Area, Attributes
File of Arcs by Polygon
1
23
4
5
6
7
8
9
10
1112
13 1 x y2 x y3 x y4 x y5 x y6 x y7 x y8 x y9 x y10 x y11 x y12 x y13 x y
Po
ints
Fil
e
1
2
2 1,8,9,10,11,12,13,7
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Tracking Topological RelationshipsTracking Topological Relationships
Connectivity– nodes bound chains– chains bound polygons
in turn,– chains are bounded by nodes– polygons are bounded by chains
A
B
C
1
2
3
4
I
II
III
IV
U
V
VI
ID Vertices From To Left RightI <list> 1 4 A UII <list> 1 2 U BIII <list> 1 3 B AIV <list> 3 2 B CV <list> 4 3 A CVI <list> 2 4 U C
ID Chains1 <list>2 <list>3 <list>4 <list>
ID ChainsA <list>B <list>C <list>U <list>
Chain table
Node table
Polygon table
ID Coorda <x,y>b <x,y>c <x,y>d <x,y>… <…>
Point table
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Typical Digitizing SituationsTypical Digitizing Situations
this is ideal, but...
overshoot, and what to do with it
undershoot, and what to do
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• Interrelationships between semantic and spatial structures
Each string is marked withleft and right labelsTrying to assemble polygonsfrom these strings: there maybe more than one label “to the left” of all strings forming a closed polygon…a standard topological error...
However, these labels maybe in container relationship in a domain map
Planar Enforcement Is Not Enough
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AutomaticAutomatic labeling results…labeling results…
12
3
4
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Special Cases: 1Special Cases: 1
B: basal nucleus of Meynert B: basal nucleus of Meynert (C0004788)(C0004788)
LGP: lateral globus pallidus, LGP: lateral globus pallidus, C0262267C0262267
Basal nucleus cells (B) are Basal nucleus cells (B) are within LGP, but their precise within LGP, but their precise locations not known locations not known polygon is coded LGP, B is a polygon is coded LGP, B is a secondary descriptorsecondary descriptor
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SpecialSpecial Cases: 3Cases: 3
DG: dentate gyrus, C0152314DG: dentate gyrus, C0152314 PoDG: polymorph layer of the dentate PoDG: polymorph layer of the dentate
gyrusgyrus CA1: field CA1 of hippocampus CA1: field CA1 of hippocampus
(C0019564)(C0019564) All of them have a common parent: All of them have a common parent:
hippocampus hippocampus a common parent is a common parent is used to label polygon; polylines are used to label polygon; polylines are labeled separatelylabeled separately