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GSP 270

GSP 270. Spatial Analysis (Vector I). Reading Assignment: Bolstad Chapter 9 (pp. 347-376). The GIS Process. Questions about the physical world. Planning: Conduct Research Define Protocols. Collect/Create/Edit Spatial Data. Create Output Report Results. Spatial Analysis.

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GSP 270

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  1. GSP 270 Spatial Analysis (Vector I) Reading Assignment: Bolstad Chapter 9 (pp. 347-376)

  2. The GIS Process Questions about the physical world • Planning: • Conduct Research • Define Protocols Collect/Create/Edit Spatial Data Create Output Report Results Spatial Analysis Spatial Analysis Decide and Act

  3. Spatial Analysis Geoprocessing Tools  Perform a Spatial Operation The output from a spatial operation may be spatial (i.e. a new data layer is produced. Or the output may be aspatial (e.g., a single value, or a table)

  4. Spatial Analysis Spatial Operations (examples): • Selection (select by attribute or by location) • Conversion between data models (e.g. vector to raster) • Buffering • Dissolving • Overlay • Clip • Intersection • Union • Erase

  5. Buffering • Creates polygons around existing vector features • ArcToolbox -> Analysis -> Proximity -> Buffer

  6. Buffers Fixed Distance Buffer • Delineates an area a fixed distance from input features (same distance).

  7. Buffers Variable Distance Buffer • Buffers at variable distances Specified by a value in Att. Table.

  8. Intersection • The overlap between two polygons Wikipedia

  9. Union • The combined area of two polygons Esri does not use this for the term “union” Wikipedia

  10. Dissolving • Dissolves features in a layer together • Based on a common attribute value • Or all features together • This is a proper Union

  11. Spatial Analysis Dissolving: • Helpful in removing unneeded information • Prior to applying an area based selection • Example: Combine drainages for each river

  12. Watershed Layer Hydrologic Unit Hydrologic Unit

  13. Output of Dissolve on Hydrologic Unit

  14. Overlay Operations Spatial Operation: Overlay Combination of separate data layers to derive new information (a new layer). Both spatial and (sometimes) attribute data are combined. (Vector Overlay -- Vineyard)

  15. Overlay Operations Slope Streams Buffer Wetlands ranked according to their vulnerability to nutrient runoff. Land Use Soils Overlay Operations

  16. Clip • “Clips” one layer with all the features from another

  17. Overlay Operations Clip: Clipping Trails Layer to Streams Buffer Identify parts of trails that are within 50 Yards of a stream

  18. Intersect • Finds the intersection of features between two or more layers

  19. Overlay Operations Intersect Case Study: Distribution of a Rare Fungal Species Habitat Requirements: • Klamath Mixed Conifer • Annual precipitation > 50 in. Goal: Find areas that meet these criteria (i.e., suitable habitat)

  20. Erase • Uses one layer to “erase” area from another layer

  21. Overlay Operations Erase Case Study: Find Legal Grazing Land (Post Ordinance). • New ordinance: No cattle grazing within 100m of a stream. • Find total amount of land where grazing would still be permitted.

  22. Split • Splits up a layer into multiple layers based on the features in the second layer

  23. Identity • “Identify” the features in one layer that overlap with features in another layer

  24. Symmetric Difference • Finds the area of features that are in one of two layers and not in the other layers

  25. Union • Combines the features from one or more layers into a single layer. The resulting features are the unique areas between the two layers (not a true Union)

  26. Update • Appears to crop the features in one layer to avoid features in another layer: • I believe the help is wrong • Not sure what this would be used for This is the actual area of the features from layer 1 (i.e. they are no longer rectangular)

  27. Append & Merge • Both these tools combine vector layers together without changing the spatial data. • Append: Adds a vector layer into another EXISTING layer • Merge: Combines multiple vector layers into a NEW layer

  28. Overlay Operations A problem in vector overlay: Multiple layers representing the same thing, or boundary line. Example: Layer 1: Incorporated areas Layer 2: Unincorporated areas The boundary differs, but represents same boundary on earth’s surface. Sliver Polygons

  29. Overlay Operations • Sliver Polygons • Take up space, but are not of any interest. • A significant increase in processing times. • Erroneous analysis results. • Remedies • Set an X,Y tolerance when you perform your overlay operation. • X,Y tolerance = a definition for the minimum tolerated distance between vertices • Forces nodes or lines to be coincident if they are within the specified X,Y tolerance. • Manually go through and remove sliver polygons • Dissolve • The “Eliminate” geoprocessing tool*. • Merges selected polygon with neighboring polys with the largest shared border or area *Requires an Advanced license.

  30. Residential Zoning Industrial Zoning Parcel

  31. Sliver Polygon

  32. Now called “X,Y Tolerance”

  33. Overlay Operations Union operation Without an X,Y Tolerance With a 10 Ft X,Y Tolerance

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