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Overview. Grid themes Setting grid theme and analysis properties Projections and grid themes Grid function types Performing grid analysis Map Algebra. Grid themes. Overview Grid theme types Grid theme properties Adding grid themes to views Displaying grid themes
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Overview • Grid themes • Setting grid theme and analysis properties • Projections and grid themes • Grid function types • Performing grid analysis • Map Algebra
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
Grid themes: Overview rectangular tessellation of square cells • Grid themes are ArcView’s implementation of the basic raster data model.
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.
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
integer floating-point • Grid themes: Grid types only integer grids have theme tables
Grid themes: The spatial analyst • All grid theme functionality occurs through the spatial analyst extension.
disk location name cell size rows &columns type status bounding coordinates • Grid themes: Grid theme properties
updated theme list new Data Source Type choice • Grid themes: Adding grid themes to views
Grid themes: Displaying grid themes usually numerically classified
Grid themes: Examining cell values in grid themes histogram shades match theme legends
Grid themes: Examining cell values in grid themes histograms can be createdfor polygonal zones
integer grid • Grid themes: Examining cell values in grid themes
integer grid • Grid themes: Examining cell values in grid themes
new menu choice • Grid themes: Managing grid theme data files (and shapefiles)
copy datasourcename rename delete sourcetype • Grid themes: Managing grid theme data files (and shapefiles)
Analysis properties determine grid theme properties for all output grid themes • Setting grid theme and analysis properties • Spatial extent • Cell size • Masking
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.
Grid function types • Global functions • Zonal functions • Focal functions
global sine • Grid function types: Global functions Global functions apply one calculation to all input grid cells.
zonal sum • Grid function types: Zonal functions Zonal functions apply one calculation to all input grid cells within each zone.
focal mean • Grid function types: Focal functions Focal functions apply one calculation to all input grid cells within a “focus.”
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
operators grid themes(layers) operator classes expression box • Performing grid analysis: Map algebra map algebra calculations are performed with GUI tools
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