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: $Date$