Raster Data and MapAlgebra Flashcards
Raster Inputs for storage
Inputs
-Spatial Analyst reads any supported raster format in ArcGIS
-Output as grids, gdb rasters, Tiff, or ERDAS
-Stores Integer or floating-point values.
Other formats (display only)
-JPEG, GIF, MrSID, raw binary, etc.
BEST PRACTICE- create a File geodatabase to store analysis outputs.
MapAlgebra
Operations using raster GIS data involve MapAlgebra
- Data structure- grid cells containing numbers
- Grid layers can be combined algebraically
- Cell by Cell Combination of Raster Data Layers
- Works well for continuous data (population, precipitation, elevation)
Con IsNull statements
Determines which values from input raster are NoData on cell-by-cell basis.
- Returns value of 1 if input value is NoData and 0 for cells that are not
- If layer A is null, use layer b. If layer A is not null, use layer c.
- Con (ISNULL(LayerA), LayerB, LayerC)
Cell statistics function in ArcMap
Helps to detect change between corresponding cells in multiple raster surfaces.
Neighborhood window operations
Calculates a statistic for a specified window within the raster.
Neighborhood focal mean and majority
Neighborhood focal mean- smooths raster, effects grow larger with increasing window size or repeated applications, good for removing noise or false values.
How do NoData values affect MapAlgebra operations?
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No Data
Specific value to indicate lack of data
-often replaced by zero in other formats
Map Algebra- Arithmetic Operators
Allow addition, subtraction, multiplication, and division
Map Algebra- Relational Operators
Allow to build logical tests, returning values of true (1) and false (0).
-Example, find vegetation “equal to” mixed coniferous forest.
Map Algebra- Boolean Operators
Such as “and”, and “or,” allow to chain logical tests, returning values of true (1) and false (0).
-Example, find all slopes that are “greater than” 45 degrees.
Map Algebra- Local Operations
Cell-to-cell correspondence: only 1 source cell contributes to the target cell value in the output layer.
Map Algebra- Neighborhood Operations
A group of nearby source cells contributes to the target cell value in the output layer.
Map Algebra- Zonal Operations
Zonal operations compute an output raster dataset where the output value for each location depends on the value of the cell at the location and the association that location has within a cartographic zone.
-For raster data, a zone is all cells with the same value.
Map Algebra- Global Operations
Global, or per-raster, operations compute an output raster dataset in which the output value at each cell location is potentially a function of all the cells combined from the various input raster datasets. Two main groups of global operations: Euclidean distance and weighted distance.
