GIS Lecture 8 Spatial Data Processing

Outline Extracting Features by Attributes Location Proximities Geoprocessing Tools Model Builder

Extracting Features

Attribute Query Extraction You have tracts for state but want one county only

Attribute Query Extraction Select tracts by County ID

Export Selected Features Right-click to export selected features

Add Exported Layer

Location Proximities

Select by Location Identify spatial relationships between layers Finds features that are within another layer. Input: County Census Tracts Can’t use Select By Attributes Output: City tracts only

Select by Location Select feature to extract tracts to (city outline)

Select by Location Selection, Select By Location

Export Selection and Add Layer

Other Select by Location Queries Toxic release sites within 1 mile of a river

Other Select by Location Queries Points near points Schools within ½ mile of polluting companies

Other Select by Location Queries Polygons intersecting lines Municipalities that intersect Interstates

Other Select by Location Queries Lines intersecting polygons

Other Select by Location Queries Buildings whose centers are in emergency zones

Geoprocessing Tools Overview Clipping Features

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

Geoprocessing Tools Clip Dissolve Intersect Union Append

Clipping Features

Clip “Cookie cutter” to select features =

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

Line (Arc) Clipping Input layer - Streets Clip layer – Central Business District (selected) Output layer - Streets within Central Business District

Clip Geoprocessing Tool

Difference Between Clipping and Select by Location Clip: Clean “cut” Select by Location: Dangle edges

Dissolving Features

Dissolve Aggregates items that have the same value # Item 1 C 2 R 3 C

Dissolve Example You have states but need regions

Dissolve Functions ArcToolBox or Command Line Window

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

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

Resultant Dissolved Regions Layer

Appending Features

Append Appends features together

Append Streets Separate street layers for neighborhoods

Append Streets Choose both street layers to append

Resultant Layer One street layer with all records and field items

Union Features

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.

Union Start with Pittsburgh ZIP codes and Neighborhoods

Union Attributes tables contain different data

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

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

Intersecting Features

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

Intersect Flood zones that intersect buildings

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

Model Builder

Model Builder Workflow processes can be complicated Automates and strings functions together

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

Model Builder Example Begin with census tracts for the state of Pennsylvania

Model Builder Example Clip only tracts whose centers are located within Pittsburgh neighborhoods Union the census tracts and neighborhoods

Model Builder Example Run the model…

Model Builder Example Display and query the results

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