## NAME

r.weight - Raster map overlay program.
(GRASS Raster Program)

## SYNOPSIS

r.weight

## DESCRIPTION

r.weight is a language driven raster map overlay program. It provides a means for performing geographical analyses using several raster maps. r.weight asks the user to weight (assign numeric values to) the raster map categories of interest. The assignment of weighted values requires that the user intimately understand the analysis being undertaken. How important is the slope of the land in comparison with the current land use, or the depth to bedrock? The assignment of values to the land's characteristics allows r.weight to mix and compare apples and oranges, such as slopes and land uses, and soil types and vegetation.

r.weight is a language-driven analysis tool. It responds to worded commands typed at the terminal. Help is always available via the one word command: help. Commands available in r.weight are listed below.

Note that raster map names appear in parentheses. The use of parentheses is now optional in r.weight.

list maps
  List available raster maps
list categories (name)
  List categories for raster map (name)
list save
  List saved analyses
list analysis
  Display current analysis request
print analysis
  Send current analysis request to printer
choose (name)
  Choose raster map (name) for analysis
assign (name)
  Interactive way to assign weights for raster map (name)
assign (name) (cat) (val)
  Assign weight (val) to category (cat) for raster map (name)
assign (name) (cat) (cat) (val)
  Assign weight (val) to categories (cat) (cat) for raster map (name)
save
  Save the current analysis
recover
  Recover old analysis
add
  Request that weights be added (this is the default)
mult
  Request that weights be multiplied
execute
  Run analysis
erase
  Erase the screen
color grey
  Set the graphics montior colors to a grey scale (this is the default)
color wave
  Set the graphics monitor colors to a color wave.
color ramp
  Set the graphics monitor colors to a color ramp.
quit
  Leave r.weight

A more detailed explanation of a command can be obtained by typing:

  help (command)

## SUGGESTED APPROACH

In order for r.weight to generate raster maps useful for analysis, the user must make a reasonable and defensible request. While much more powerful than r.combine, r.weight is also more dangerous. The user provides the necessary value judgements which are registered as weights. Only well-conceived value judgements will result in defensible results. We suggest the following approach to a weighted overlay analysis:

STEP 1: BEFORE RUNNING WEIGHT
  a)
    Define the question to be answered. e.g., "Locate sites suitable for building apartments."
  b)
    Determine what mapped information is useful for answering the question. e.g., geology, soils, land_use, flood_potential.
  c)
    Based on professional judgement, statistical inference, and engineering principals, assign weights to the categories in the chosen raster maps.
STEP 2: CHOOSE CELL MAPS

  In r.weight, use the command choose to identify up to six raster maps of interest.

STEP 3: ASSIGN WEIGHTS

  Using the r.weight command assign, assign specific weights to raster map categories.

STEP 4: SAVE ANALYSIS

  Use the save command to save a copy of the analysis requested for later use.

STEP 5: RUN ANALYSIS

  Use execute to run the analysis.

STEP 6: EVALUATE RESULTS

  To modify an existing analysis request, use the recover command to retrieve the analysis and then go to STEP 3.

## SEE ALSO

GRASS Tutorial: r.weight

r.infer
r.combine
r.mapcalc

## AUTHOR

James Westervelt, U.S.Army Construction Engineering Research Laboratory

Last changed: $Date: 2002/01/25 05:45:34 $