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Grid Themes: Overview, Types, Properties, and Analysis

Discover the basics of grid themes in ArcView, including different types, properties, and how to perform grid analysis using map algebra. Explore spatial extent, cell size, masking, and projection considerations.

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Grid Themes: Overview, Types, Properties, and Analysis

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Presentation Transcript

  1. Overview • Grid themes • Setting grid theme and analysis properties • Projections and grid themes • Grid function types • Performing grid analysis • Map Algebra

  2. Grid themes • Overview • Grid theme types • Grid theme properties • Adding grid themes to views • Displaying grid themes • Examining cell values in grid themes • Managing grid theme files

  3. Grid themes: Overview rectangular tessellation of square cells • Grid themes are ArcView’s implementation of the basic raster data model.

  4. cell values are displayed in the legend • Grid themes: Overview • each cell has a numeric value • Grid themes are ArcView’s implementation of the basic raster data model.

  5. Grid themes: Overview • Grid themes are good for representation of phenomena that vary gradually over space such as elevation, wind speed and direction, or slope

  6. integer floating-point • Grid themes: Grid types only integer grids have theme tables

  7. Grid themes: The spatial analyst • All grid theme functionality occurs through the spatial analyst extension.

  8. disk location name cell size rows &columns type status bounding coordinates • Grid themes: Grid theme properties

  9. updated theme list new Data Source Type choice • Grid themes: Adding grid themes to views

  10. Grid themes: Displaying grid themes usually numerically classified

  11. Grid themes: Examining cell values in grid themes histogram shades match theme legends

  12. Grid themes: Examining cell values in grid themes histograms can be createdfor polygonal zones

  13. integer grid • Grid themes: Examining cell values in grid themes

  14. integer grid • Grid themes: Examining cell values in grid themes

  15. new menu choice • Grid themes: Managing grid theme data files (and shapefiles)

  16. copy datasourcename rename delete sourcetype • Grid themes: Managing grid theme data files (and shapefiles)

  17. Analysis properties determine grid theme properties for all output grid themes • Setting grid theme and analysis properties • Spatial extent • Cell size • Masking

  18. Setting grid theme and analysis properties: Spatial extent

  19. Setting grid theme and analysis properties: Cell size

  20. Setting grid theme and analysis properties: Masking

  21. Setting grid theme and analysis properties: Masking

  22. Projections and grid themes ArcView cannot project grid themes on the fly as it projects feature themes. • Do not view unprojected grid themes with projected vector themes. • View projected grid themes with unprojected vector themes by setting view projection properties. • If you need to project a grid theme to match projected vector themes, use ARC/INFO.

  23. Grid function types • Global functions • Zonal functions • Focal functions

  24. global sine • Grid function types: Global functions Global functions apply one calculation to all input grid cells.

  25. zonal sum • Grid function types: Zonal functions Zonal functions apply one calculation to all input grid cells within each zone.

  26. focal mean • Grid function types: Focal functions Focal functions apply one calculation to all input grid cells within a “focus.”

  27. Performing grid analysis: Map algebra (or “How it works”) • multiple grid themes share the same X, Y coordinate space • cell values are calculated across multiple grid themes

  28. operators grid themes(layers) operator classes expression box • Performing grid analysis: Map algebra map algebra calculations are performed with GUI tools

  29. Performing grid analysis: Map algebra (or “How it works”) grid themes may be used in algebraic functions output_data_set = function (input_data_set(s) {,arguments}) slp_grid = slope (dem, percentrise) grid themes may be used in algebraic expressions output_data_set = input_grid1 operator input_grid2 . . . slp_dem = slp_grid * dem

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