Map Algebra

Local Functions

• work on single cells sequentially
• ex: elementwise products

Focal Functions

• assign data value to a cell based on its neighborhood
• Uses smoothing / moving average, edge detection
• ex: focal sum (sum all values in neighborhood )
• focal mean

Zonal Functions

• assign values to all cells in a zone, based on values from another map

Global / Incremental Functions

• Cell value for each cell depends on processing entire gird (relativity)
• ex: computing distance from one cell to all other cells
• distance can be weighted
• Uses: diffusion modeling, shortest paths, visibility

Simplest Operations

• one map, cell by cell
• Reclassify: reduce information content (selection, classifcation), increase information content (ranking, scaling)
• in vector form some geometric processes may be required