GIS Lecture 8

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GIS Lecture 8 Spatial Data Processing
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Outline

• Extracting Features by Attributes
• Location Proximities
• Geoprocessing Tools
• Model Builder

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Extracting Features
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Attribute Query Extraction

• You have tracts for state but want one county only

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Attribute Query Extraction

• Select tracts by County ID

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Export Selected Features

• Right-click to export selected features

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Add Exported Layer
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Location Proximities
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Select by Location

• Identify spatial relationships between layers
• Finds features that are within another layer.

Input County Census TractsCant use Select By
Attributes
OutputCity tracts only
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Select by Location

• Select feature to extract tracts to (city outline)

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Select by Location

• Selection, Select By Location

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Export Selection and Add Layer
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Other Select by Location Queries

• Toxic release sites within 1 mile of a river

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Other Select by Location Queries

• Points near points
• Schools within ½ mile of polluting companies

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Other Select by Location Queries

• Polygons intersecting lines
• Municipalities that intersect Interstates

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Other Select by Location Queries

• Lines intersecting polygons

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Other Select by Location Queries

• Buildings whose centers are in emergency zones

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Geoprocessing Tools OverviewClipping Features
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Geoprocessing Tools

• GIS Operation to manipulate data
• Typically take input data sets, manipulate, and
  produce output data sets
• Often use multiple data sets

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Geoprocessing Tools

• Clip
• Dissolve
• Intersect
• Union
• Append

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Clipping Features
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Clip

• Cookie cutter to select features

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Clipping Features (Points, Lines, Polygons)
X Y Z



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Line (Arc) Clipping

• Input layer - Streets
• Clip layer Central Business District (selected)
• Output layer - Streets within Central Business
  District

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Clip Geoprocessing Tool
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Difference Between Clipping and Select by Location
Clip Clean cut
Select by LocationDangle edges
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Dissolving Features
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Dissolve

• Aggregates items that have the same value

Item 1 C 2 R 3 C 4 I
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Dissolve Example

• You have states but need regions

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Dissolve Functions

• ArcToolBox or Command Line Window

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Dissolve Field

• Field with a common value for each feature (e.g.
  Sub_Region)

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Statistics Field

• Aggregated field can be summarized using a
  statistics type (i.e. state population can be
  aggregated by population for each region)

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Resultant Dissolved Regions Layer
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Appending Features
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Append

• Appends features together

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Append Streets

• Separate street layers for neighborhoods

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Append Streets

• Choose both street layers to append

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Resultant Layer

• One street layer with all records and field items

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Union Features
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Union

• Use Union when you want to overlay two polygon
  layers so that the resulting output layer
• a) has the combined attribute data of the
  polygons in the two inputs, and
• b) contains all the polygons from the inputs,
  whether or not they overlap.

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Union

• Start with Pittsburgh ZIP codes and Neighborhoods

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Union

• Attributes tables contain different data

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Union

• Union neighborhoods and ZIP Codes to include the
  zip on each neighborhood polygon

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Union

• Result Polygons are unioned with same
  information
• Tips Same Projections, Order of Layers

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Intersecting Features
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Intersect

• Use Intersect when you want to overlay a layer
  with the polygons in another layer so that the
  resulting output layer
• - has the combined attribute data of the features
  in the two inputs, and
• - only contains features that fall within the
  spatial extent of the overlay polygons

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Intersect

• Flood zones that intersect buildings

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Intersect

• Result is only building polygons that intersect
  floodzones with combined data fields

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Model Builder
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Model Builder

• Workflow processes can be complicated
• Automates and strings functions together

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Model Builder

• Problem
• You have census tracts from a state with
  population data but only want population for
  neighborhoods in a small region
• Solution
• Use Model Builder functions to clip census tracts
  and union to aggregate data to neighborhoods

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Model Builder Example

• Begin with census tracts for the state of
  Pennsylvania

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Model Builder Example

• Clip only tracts whose centers are located within
  Pittsburgh neighborhoods
• Union the census tracts and neighborhoods

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Model Builder Example

• Run the model

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Model Builder Example
Display and query the results
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Summary

• Extracting Features
• Attribute Queries
• Select by Location
• Converting Shapefiles
• Geoprocessing Tools
• Clip
• Dissolve
• Union
• Intersect
• Append
• Model Builder