vectoranalysis 6th semester

8/2/2019 VectorAnalysis 6th semester

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Foundations for Applied GIS

Vector Spatial Analysis

Geog-3205

By

Khurram Chohan


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Review

Functions of a GIS


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Overview

Spatial data analysis What is spatial analysis?

Focusing your analysis: Queries and selections

Running your analysis: Spatial functionsSingle layer operations: Buffering, summarizing

Multiple layer functions: splitting, merging, overlay

Models

Specialized forms of analyses

Point pattern analysis

Network analysis


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Spatial analysis process

Frame the question

Understand your data

Choose a method

Process the data

Look at the results

Common GIS Analysis Tasks: Mapping where things are Mapping most and least Finding whats inside Finding whats nearby

GIS Analysis Examples: Finding features affected byproposed road

Getting driving directionsfrom MapQuest

Based on Mitchell (1999): The ESRI Guide to GIS Analysis (on reserve)


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Focusing Analysis: Queries and selections

Selection: Finding features that meet conditions orcriteria

Which businesses are in Punjab Province?

Which city businesses are within 5 mi of Railway station? Calculate distance between two cities (Karachi to

Hyderabad )


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Queries in GIS

Query: question to get info about your database Types of queries:

Aspatial (based on table): Select by attributes

Spatial (based on geometry): Select by location

Attribute: characteristic of a feature

Logic of queries:

Create new

selection

Remove from

the selection

Add to theselection

Select fromselection


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Parts of Query

Relational operators

= < > =

Boolean/logical operators

AND OR NOT

Simple queries

Punjab= Lahore

Compound queries

House_Size >20marla AND Lawn=yes

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Working with query results

Why select features? Focus your analysis

Use selected features to select other features (from other

layers) Save selected set to a new dataset

Summarize selected features


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Spatial analysis functions

One or more inputs

One or more outputs

Input/outputs may be spatial (layers) or other types

of data, such as tables, values, or lists

Functions may be grouped together into a model


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Spatial operations

Bolstad (2008): Figure 9-2 (on reserve)


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Single-layer analysis functions

Data generalization: Summarize, dissolve Combining your data into simpler format

Proximity analysis: Buffering

Finding whats nearby


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Summarize

Attribute summarization Count number of features

Count number of features by type

Summarize other numeric attributes (area, length, etc.)

Useful for reporting results of analysis


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Example: Summarize attributes

Summarize by location Summarize by type

Results in table

State # TornadoesTexas 178

Kansas 125

Iowa 119

Nebraska 109

West Virginia 5

Tornadoes (2004)National Atlas

State # Tornadoes

Texas 178

Kansas 125

Iowa 119

Nebraska 109

West Virginia 5


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Example: Summarize attributes

Summarize by location Summarize by type

Results in table

Tornadoes (2004)by Fujita scale (severity)

F scale # Tornadoes

0 1214

1 470

2 103

3 23

4 5


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Dissolve function

Spatial summarization

Remove unneeded information

Simplify your data

Group like features into single larger feature


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Example: Dissolve

343 watersheds (before)With river basin attribute

32 river basins (after)New shapefile


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Proximity analysis: Buffering

Proximity: distance between features

Buffer: area at a given distance from mappedfeatures (inside or outside a threshold distance)

How buffering works:

Buffer points, lines, polygons at a certain distance

Can dissolve adjacent buffers, or keep separate

Can buffer all at same distance, or can vary distance


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Example: Buffer

Can buffer points, lines or polygons

Multiple 5 mile buffer zones

around Charleston

1 mile buffer around Blackwater River


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Example: Buffer

Buffer with Dissolve Buffer without Dissolve

Schools buffered by mile


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Example: Buffer

Create buffers

Then, use buffers to clip other layers

Mile Buffer, University High School

Used to clip roads layer


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Multiple-layer functions

Overlay analysis Clip

Intersect

Union

Clip Intersect

Union


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Example: Clip

Streams Watershed Clip Result


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Example: Clip

I-64922 miles total

I-64After clip to WV

180 miles

Remember to update length, area, perimeter etc. after clip


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Example: Intersect

Intersect combines features, only in area commonto both layers

Features in output layer have attributes of both

layers

Monongahela

NationalForest

RangerDistricts and

Roads

RoadsIntersected

With Districts


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Example: Union

Union combines features from two polygon layers Output includes all attributes from both input layers

Great LakesRegion

Union output:All features aremaintained, but

are split


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Other multi-layer functions

Erase Spatial join

Merge

Erase


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Example: Spatial join

Two layers Input features (usually points) are labeled with all

attributes of all join layer features

Springs

Springsjoined with

County


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Example: Merge

Two or more input layers (must be same featuretype)

Merge into single output layer

Streams (in two

adjacent watersheds)

Streams (merged)


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Problems in layer overlay

Slivers, layers dont always overlay exactly ArcGIS: layers need to have defined projections

Watersheds

slivers


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Example: Multi-part analysis

Many questions require multiple steps to be carriedout in sequence:

Selecting features

Performing single or multiple layer functions

For example:

How many acres of emergent wetlands are within 1/10thmile of the proposed highway route?


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Sample question: Steps

Input layers

Wetlands

HighwayRoute

Buffer by 0.1mile

Selectemergent

wetlands only

EmergentWetlands

Road buffer

Clip

ClippedEmergentWetlands

RecalculateArea after clip

Summarizearea of allpolygons

Answer

Analysis functionsIntermediate

output layers


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Analysis in ArcGIS software: ArcToolbox

ArcToolbox contains all analysis functionsdiscussed, plus many more

ArcToolbox runs within ArcMap

All functions grouped into categories,wizard-driven

For best results:

Install latest patch (if using student evaluationsoftware)

Make sure all layers have projection defined


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Analysis in ArcGIS: Models

ArcGIS can also automate models using Models(in ArcToolbox)

Why build model?

More efficient way to run repetitive tasks

Re-run same steps with different data layers

Can model complex processes

Input Data Tool Derived Data


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Model Builder example

ILARIS model: Ranking signature landscapes forPuget Sound

60 input layers

40 sub-models


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Mine permits and coal seams

Analyzing spatial patterns: Spatial statistics

Point pattern analysis: Are locations random or clustered?

Tests

Randomness

Clustering

Spatial autocorrelation


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Point pattern analysis: Clustering

Nearest neighbor analysis Are your points dispersed or clustered?

Function in ArcGIS


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Point pattern analysis: Auto-correlation

Spatial auto-correlation: Features closer to oneanother are more related than features further away

Morans I: A measure of spatial auto-correlation

Function found in ArcGISA larger positivenumber = -1 = a scattered pattern


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Other point analyses

Can compute point-to-point distance As the crow flies (straight line)


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Network analysis

Network: System of connected lines Network attributes for each segment:

Direction

Length Connectivity

Forms of network analysis:

Network navigation (paths) along network Distance, travel cost, route selection

Linear referencing/addressing


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Networks in GIS

Stream flow network Road network


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Network analysis: Distance along network

With network: Distance from point to point

Estimate time of travel

Navigate upstream/downstream

Direction of flow

Town

Spill

How far?How long?


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Network analysis: Route selection

MapQuest


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Network analysis: Linear referencing

GIS can be used to automatically locate streetaddresses

Needs:

Table of addresses to locate

Streets layer

From address attribute

To address attribute

Example:Locating 321 M.L.King Street

Figure 9-45, Bolstad (2008)


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Learning more

Specialized GIS analyses are covered in moredetail

RESM follow up classes (Natural/Social Science)

RESM 575 (taught spring semester) ESRI Virtual Campus classes (see link)

Network Analyst

Spatial statistics

Address geo-coding

Free to WVU students (check website, then see me to sign up)

http://training.esri.com/campus/catalog/licenses/courselist.cfm?id=43
http://training.esri.com/campus/catalog/licenses/courselist.cfm?id=43http://training.esri.com/campus/catalog/licenses/courselist.cfm?id=43


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vectoranalysis 6th semester

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