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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=438/2/2019 VectorAnalysis 6th semester
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