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GIS Lecture 8Spatial 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 TractsCan’t use Select By Attributes

Output:City 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 QueriesPolygons intersecting linesMunicipalities that intersect Interstates

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Other Select by Location QueriesLines 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 LocationClip: Clean “cut”

Select by Location:Dangle edges

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Dissolving Features

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Dissolve Aggregates items that have the same value

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Item1

C2

R3

C4

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 FieldField 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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UnionStart 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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IntersectFlood 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 ExampleDisplay 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