@ 2007 Austin Troy

@ 2007 Austin Troy

Geoprocessing

Introduction to GIS

• Geoprocessing is the processing of geographic information.

– Creating new polygon features through buffering (e.g. Buffer)

– Breaking features into smaller features (e.g. Clip, Intersect, Union)

• Three general classes of tools

– Aggregating features into larger features (e.g. Dissolve,Merge)

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Introduction to GIS

Geoprocessing

Slide courtesy of Leslie Morrissey

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Introduction to GIS

Geoprocessing in ArcGIS• Perform geoprocessing in ArcGIS

– Create and run a script

– Run tools at a command line.

– Run a tool using its dialog box.

– Build and run a model

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Introduction to GIS

Geoprocessing in ArcGIS• Perform geoprocessing in ArcGIS

– Create and run a script

– Run tools at a command line.

– Build and run a model

– Run a tool using its dialog box.

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Tools: GeoprocessingTools for breaking down the size of map

features: Union, Intersect, Identity, Clip

Tools for increasing the size of map features:Dissolve and Merge (indirectly)

Arc/Info and Arc Toolbox include various other geoprocessing overlay operations, such as Update and Dissolve Regions

Introduction to GIS

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UnionCombines features of two or several themes

Keeps all line workBreaks down features, and creates new

polygonsKeeps all attributes

Introduction to GIS

Image source: ESRI Arc Info electronic help

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Tools: Union

Introduction to GIS

Polygons only

A list of Polygons

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Find the Geoprocessing Tools

Introduction to GIS

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IntersectYields areas that are common to both

layersPreserves line work within common extent Usually creates many new, smaller polygonsPreserves all attributes from both

Introduction to GIS

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Tools: Intersect

Introduction to GIS

Two layers

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Union vs. IntersectionUnion is the union of two overlapping set of

features and intersection is the intersection

Introduction to GIS

Layer 1 + Layer 2

Intersect: “1 AND 2”

“1 OR 2”Union:

Layer 2Layer 1 +

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Union vs. Intersection: ExampleHere’s an example. Say we have deer

wintering areas in one layer and conserved lands in another.

Introduction to GIS

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Union vs. Intersection: ExampleUnion gives us land that is EITHER

conserved OR that is a deer wintering areas

Introduction to GIS

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Union vs. Intersection: ExampleIntersect gives us land that is BOTH, and preserves

all polygon boundaries within that common extent

Introduction to GIS

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IdentityIdentity performs an intersection but doesn’t

retain ALL featuresKeeps all “input” layer featuresKeeps/creates only overlapping “identity” features

and their attributes

Introduction to GIS

Kept, as with union

Common (intersecting) areas

Not kept, as with intersect

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ClipThis uses one theme to “clip,” or serve

as the outer boundary of another themeBreaks down features into smaller unitsPreserve the input theme’s attributes

Introduction to GIS

Point, line, or polygon

Polygon only

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Tools: Clip

Introduction to GIS

Point, line,

polygon

Polygon

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Clipping highways for Merced

Introduction to GIS

Note that the “use selected features only” option was used

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Clipping roads

Introduction to GIS

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DissolveTool for aggregating polygons—making

them bigger. Single layer operation

Introduction to GIS

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Tools: Dissolve

Introduction to GIS

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Dissolve: ExampleDissolve zip codes (small) into counties

(large)

Introduction to GIS

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Dissolve: ExampleChoose the dissolve field: e.g. Dissolve

based on the County field

Introduction to GIS

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Dissolve : Example

Introduction to GIS

• Summarize the resulting field values. For instance, you could sum population for each county, or average size of ZIP code zones for each county

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Dissolve : ExampleNow we have

created a county map, and for each county we have an attribute containing the sum of population of the constituent zip codes

Introduction to GIS

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MergeAllows you to “join” two adjacent or non-

adjacent themes into the same layerLike “tiling”Best when attributes match

Introduction to GIS

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Tool: Merge

Introduction to GIS

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MergeOften when you merge you will want to

follow up by dissolving.

Introduction to GIS

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Tools: BufferingBuffering is when you draw a polygon

around a feature (point, line or polygon)

Introduction to GIS

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Tools: Buffering

Introduction to GIS

Based on distance

Based on attribute

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Tools:Variable Width Buffering

Introduction to GIS

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Combining Geoprocessing Tools Involve multiple tasks performed in sequence,

such as those that clip, buffer, intersect, union, then select datasets.

Introduction to GIS

– Create and run a script

– Build and run a model

– Step by step

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Combining Buffering and Geoprocessing: Example

Question: How to find areas that are near deer wintering areas and water bodies but far from traffic?

Geospatial DataPolygon layer for deer wintering areas Polygon layer for Water bodiesRoads layer: line features

Introduction to GIS

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Combining Buffering and Geoprocessing: Example

Question: How to find areas that are near deer wintering areas and water bodies but far from traffic?

Introduction to GIS

– Areas that are near deer wintering areas AND water bodies:– Combining the layers:

Intersect

– “Near” or “Far from”: Buffering

Union– Selecting: Query for areas that are not within a traffic buffer

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Combining Buffering and Geoprocessing: Example

Buffering: Made fixed buffers around deer wintering areas and water bodies, and a variable buffer around roads, based on traffic

Introduction to GIS

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Combining Buffering and Geoprocessing: Example

Intersecting: The intersection of deer wintering buffers and water buffers (the area in the red)

Introduction to GIS

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Combining Buffering and Geoprocessing: Example

The union of that intersection with the traffic buffer:

Introduction to GIS

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Combining Buffering and Geoprocessing: Example

Selecting: Query for polygons that are not within (far from) a traffic buffer

Introduction to GIS

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Combining Buffering and Geoprocessing: ExampleCreate a new

layer by exporting the selected features (polygons)

Introduction to GIS

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Geoprocessing Summary

Introduction to GIS

Union Intersect Identity Clip Dissolve Merge Buffer