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Raster Analysis Techniques for Effective Spatial Data Management

Explore raster analysis tools for topography, statistics, and conversions. Learn local, neighborhood, and zonal statistics methods. Discover Jim's secrets for raster processing and data management tips.

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Raster Analysis Techniques for Effective Spatial Data Management

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  1. Raster Analysis • Raster math • Topography: Slope, aspect, contours • Reclassify • Raster / Vector Conversions • Statistics: min, max, mean, std. dev. • Local, Neighborhood, Zonal • Histograms • No Data / Null Value Issues • Future: • Distance (cost)

  2. Jim’s Secrets for Rasters • Keep the overall size of the rasters below 200 Meg • Use “Resample” to convert to relatively small “IMG” files (or GRIDS) • Data Management Tools -> Raster -> Raster Processing -> Resample • Watch “Results” for errors • Geoprocessing -> “Results” • Use “Task Manager” when Arc crashes

  3. Task Manager • Right Click on Menu Bar, “Start Task Manager” • “End Process” on all “Arc” processes

  4. Raster Statistics • Local • Operate on one pixel in each raster • Neighborhood (or Focal) • Operate on a few pixels around each pixel • Zonal • Collection of regions • Region is a contiguous area of the same pixel values • Global • Operate on the “whole” raster

  5. Local Stats • “Cell Statistics” computes stats on all the values for a pixel in a multi-band raster. • Example for “Sum”: Esri ArcGIS 10 Help

  6. Neighborhood (or Focal) • Result=Operation on pixels nearby Columns Rows

  7. Focal Statistics • Computes stats on pixels around an existing pixel • Example for Sum: Esri ArcGIS 10 Help

  8. Zonal Statistics • Computes statistics for defined regions (features) • Tools: • Zonal Statistics: • Outputs a raster (not sure of the value) • Zonal Statistics as Table: • Outputs a table • Used to compute all kinds of valuable things: • Percent land cover • Percent impervious cover • Percent water below a certain depth • Etc.

  9. Zonal Statistics Zone Layer Value layer Output layer (or table) Esri ArcGIS 10 Help

  10. Conditional Operator • Con(<condition>,<true>,<false>) • Given a raster “condition”: • Puts the true value where true and false value where false Con!

  11. Elevations over 3000 meters • Con("W100N40.DEM“>3000,0,1)

  12. Elevations over 3000 meters

  13. Issues with No Data

  14. Issues with Signed Data

  15. Convert Values to “No Data” SetNull("W100N40.DEM"==55537,"W100N40.DEM")

  16. Rasters Draw as “Solid” Color • Click on “Type:” and select “Minimum-Maximum” • ArcGIS will compute statistics

  17. Histograms

  18. Exporting Histograms

  19. Titles and Axis Labels!

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