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Grid-Based GIS Map Functions

By Michael N. DeMers

Part of GIS For Dummies Cheat Sheet

If your GIS (geographic information system) is grid-based, you have access to some cool, algebra-based functions. The following table shows the functions, where they work, and what you can do with each:

Function Type Where It Operates What It’s Used For
Local On individual grid cells To change cell values based on user definition or the value of
corresponding grid cells on other layers.
Focal On a specifically targeted grid cell To return a value (such as an average) based on the values of
neighboring grid cells
Zonal On grid cells in specifically identified regions To calculate values based on analysis of specified regions that
are not necessarily connected
Block On square blocks of grid cells To return a value for the identified block (for example, a 4 x
4 block of cells) on an output grid
Global On the entire grid To highlight hard-to-find features and spot general trends by
moving through the entire grid
Specialty On specified grid cells To perform high-end statistical analysis or create models for
moving surfaces (such as water or pollution)