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@ 2007 Austin Troy
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Geoprocessing Introduction to GIS Geoprocessing is the processing of geographic information. Perform spatial analysis and modeling via tools that transform datasets Includes methods to automate GIS workflows
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@ 2007 Austin Troy Geoprocessing Introduction to GIS – 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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@ 2007 Austin Troy 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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@ 2007 Austin Troy Introduction to GIS Geoprocessing in ArcGIS Several ways to do this…. – 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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@ 2007 Austin Troy Finding Geoprocessing Tools Introduction to GIS
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@ 2007 Austin Troy Introduction to GIS Vector Overlay Functions Slide courtesy of Leslie Morrissey
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@ 2007 Austin Troy Union Combines features of two or several themes Keeps all line work (extent contains both inputs) Breaks down features, and creates new polygons Keeps all attributes Polygon only (no points/lines) Introduction to GIS Image source: ESRI Arc Info electronic help
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@ 2007 Austin Troy Tools: Union Introduction to GIS Polygons only A list of Polygon datasets
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@ 2007 Austin Troy Intersect Yields areas that are common to both layers Preserves line work within common extent Usually creates many new, smaller polygons Preserves all attributes from both Polygon overlaid with… Polygon Line (output: line) Point (output: point) Introduction to GIS
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@ 2007 Austin Troy Tools: Intersect Introduction to GIS Two layers
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@ 2007 Austin Troy Union vs. Intersection Union is the complete combination of two overlapping sets of features and intersect is the intersection of inputs (only the overlapping parts) Introduction to GIS Layer 1 +Layer 2 Intersect: “1 AND 2” “1 OR 2” Union: Layer 2Layer 1 +
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@ 2007 Austin Troy Union vs. Intersection: Example Here’s an example. Say we have deer wintering areas in one layer and conserved lands in another. Introduction to GIS
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@ 2007 Austin Troy Union vs. Intersection: Example Union gives us land that is EITHER conserved OR that is a deer wintering areas Introduction to GIS
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@ 2007 Austin Troy Union vs. Intersection: Example Intersect gives us land that is BOTH, and preserves all polygon boundaries within that common extent Introduction to GIS
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@ 2007 Austin Troy Identity Identity performs a special type of intersection Keeps all “input” features and attributes but only overlapping “identity” features and their attributes First (“input”) layer determines geographic extent Polygon with polygon, point, or line Introduction to GIS Kept, as with union Common (intersecting) areas Not kept, as with intersect
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@ 2007 Austin Troy Overlay trouble warning…. Output layer combines spatial polygons and attribute tables Introduction to GIS Overlay ParcelsImpervious/Pervious Yikes! Zillions of polygons! Illustrative material courtesy of Leslie Morrissey
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@ 2007 Austin Troy Overlay trouble warnings…. Can result in polygon slivers Yikes! Output file type (shapefile vs. feature class) Shapefile output: no recalculation of area, perimeter, or length fields Double yikes! Output as GDB feature class for accurate area, perimeter, and length calculations! Input layers must have matching projection/datum (spatial reference) No automatic recalculation of numeric attributes for polygons that depend on a spatial unit! More error! Introduction to GIS Slide content courtesy of Leslie Morrissey
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@ 2007 Austin Troy Overlay attribute errors All input layer attributes are preserved as is Population is attributed to each output polygon Count is not recalculated proportional to area Total population for output is wrong! Introduction to GIS States CountryOutput + = Population = 9 million A C B D A+ 9M C+ 9M B+ 9M D+ 9M Sum Pop. = 36M?? Uh oh! Slide content courtesy of Leslie Morrissey
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@ 2007 Austin Troy Clip This uses one theme to “clip,” or serve as the outer boundary of another theme Breaks down features into smaller units Preserves the input theme’s attributes Introduction to GIS Point, line, or polygon Polygon only
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@ 2007 Austin Troy Tools: Clip Introduction to GIS Point, line, polygon Polygon
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@ 2007 Austin Troy Clipping highways for Merced Introduction to GIS Note that the “use selected features only” option was used
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@ 2007 Austin Troy Clipping roads Introduction to GIS
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@ 2007 Austin Troy Dissolve Tool for aggregating polygons—making them bigger. Single layer operation Introduction to GIS
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@ 2007 Austin Troy Tools: Dissolve Introduction to GIS
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@ 2007 Austin Troy Dissolve: Example Dissolve zip codes (small) into counties (large) Introduction to GIS
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@ 2007 Austin Troy Dissolve: Example Choose the dissolve field: e.g. Dissolve based on the County field Introduction to GIS
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@ 2007 Austin Troy 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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@ 2007 Austin Troy Dissolve : Example Now 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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@ 2007 Austin Troy Merge Allows you to “join” two adjacent or non-adjacent themes into the same layer Like “tiling” Best when attributes match Introduction to GIS
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@ 2007 Austin Troy Tool: Merge Introduction to GIS
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@ 2007 Austin Troy Merge Often when you merge you will want to follow up by dissolving. Introduction to GIS
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@ 2007 Austin Troy Tools: Buffering Buffering is when you draw a polygon around a feature (point, line or polygon) Introduction to GIS
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@ 2007 Austin Troy Tools: Buffering Introduction to GIS Based on distance Based on attribute
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@ 2007 Austin Troy Tools:Variable Width Buffering Introduction to GIS
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@ 2007 Austin Troy More Overlay Tools Introduction to GIS Update – merge new features, e.g., add new parcel to parcels layer Erase – remove some interior portion of a layer Some content courtesy of Leslie Morrissey
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@ 2007 Austin Troy 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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@ 2007 Austin Troy Combining Buffering and Geoprocessing: Example Question: How to find areas that are near deer wintering areas and water bodies but far from traffic? Geospatial Data Polygon layer for deer wintering areas Polygon layer for Water bodies Roads layer: line features Introduction to GIS
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@ 2007 Austin Troy 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 – A reas 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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@ 2007 Austin Troy 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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@ 2007 Austin Troy 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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@ 2007 Austin Troy Combining Buffering and Geoprocessing: Example The union of that intersection with the traffic buffer: Introduction to GIS
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@ 2007 Austin Troy 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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@ 2007 Austin Troy Combining Buffering and Geoprocessing: Example Create a new layer by exporting the selected features (polygons) Introduction to GIS
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@ 2007 Austin Troy Flow Chart for Analysis Introduction to GIS Deer wintering areas Intersect Water Traffic Buffer Deer_buffWater_buffTraffic_buff Union Deer wintering & water buffers Deer/water buffers plus traffic buffer Select Export Buffer Deer/water buffers away from roads
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@ 2007 Austin Troy Geoprocessing Summary Introduction to GIS UnionIntersectIdentityClipDissolveMergeBuffer
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