## DESCRIPTION

v.colors allows the user to create and/or modify the color table for a vector map. The vector map (specified on the command line by map) must exist in the user's current mapset search path.

As input a vector map with a numeric data column is required which is used to apply the color rules. The color values are stored in a string column (default name "GRASSRGB", varchar(11)) by saving the RRR:GGG:BBB values suitable for use with '`d.vect -a`'. If this RGB column is not found in the attribute table, it is automatically created.

The rast option allows user to specify a raster map name from which to copy the color map.

The volume option allows user to specify a volume (3D raster) map name from which to copy the color map.

If the user specifies the -w flag, the current color table file for the input map will not be overwritten. This means that the color table is created only if the map does not already have a color table. If this option is not specified, the color table will be created if one does not exist, or modified if it does.

In general, tables which associate colors with percentages (aspect, bcyr, byg, byr, elevation, grey, gyr, rainbow, ramp, ryb, ryg and wave) can be applied to any data, while those which use absolute values (aspectcolr, curvature, etopo2, evi, ndvi, population, slope, srtm, and terrain) only make sense for data with certain ranges. One can get a rough idea of the applicability of a colour table by reading the corresponding rules file (`$GISBASE/etc/colors/<name>`). For example the ryg rule is defined as:

    0% red
    50% yellow
    100% green

The rules color table type will cause r.colors to read color table specifications from standard input and will build the color table accordingly.

For details see r.colors manual page.

## EXAMPLES

Define color table `wave` based on categories from layer 1

    v.colors map=soils_general layer=1 color=wave

Define color table `ryg` based on values from attribute column `AREA`. Attribute table is linked to layer 1.

    v.to.db map=soils_general layer=1 option=area column=AREA
    v.colors map=soils_general layer=1 color=wave column=AREA

Write color values to the attribute table (column `GRASSRGB`) instead of creating color table.

    v.colors map=soils_general layer=1 color=wave column=AREA rgb_column=GRASSRGB

    # See some GRASSRGB values:
    v.db.select map=soils_general | head -n 4
    cat|OBJECTID|AREA|PERIMETER|GSLNC250_|GSLNC250_I|GSL_NAME|GRASSRGB
    1|1|0|164616.125|2|1|NC113|212:42:127
    2|2|0|30785.529297|3|2|NC096|212:42:127
    3|3|0|87572.882812|4|3|NC097|212:42:127

Convert existing RGB values to color table rules.

    v.colors -c map=soils_general rgb_column=GRASSRGB

Note that in this case the vector map has a proper color table assigned (check by v.colors.out) together with GRASSRGB attribute column. Also note that color table is prefered over RGB values stored in attribute table.

Existing color table can be removed by -r flag.

    v.colors -r map=soils_general

Before removing color table you can store color rules to the file by v.colors.out and later to assign by rules option.

    v.colors.out map=soils_general > soils.colr
    v.colors map=soils_general rules=soils.colr

To drop RGB column use v.db.dropcolumn.

    v.db.dropcolumn map=soils_general column=GRASSRGB

## SEE ALSO

d.vect, v.colors.out, r.colors, r.colors.out, r3.colors, r3.colors.out,

See also wiki page Color tables (from GRASS User Wiki)

ColorBrewer is an online tool designed to help people select good color schemes for maps and other graphics.

## AUTHORS

Martin Landa, Czech Technical University in Prague, Czech Republic

Last changed: $Date$