## DESCRIPTION

d.vect.thematic draws thematic choropleth vector maps based on an attribute column or an expression involving several columns. It takes a list of class breaks (excluding the minimum and maximum values) and a list of colors to apply to the classes (has to be the number of class breaks + 1).

Instead of a list of class breaks, the user can also chose a classification algorithm and a number of classes (nbclasses). See the v.class for more information on these different algorithms.

Important note: The module currently supports only area vector type. For displaying thematic choropleth vector maps of other types (points, lines) can be used d.vect.thematic2 available in AddOns via g.extension.

## NOTES

The -l flag instructs the module to print legend information (class min | class max | number of observations in class | color) to standard output for futher use in graphical software. When combined with the -e flag, the legend information will be extended with some additional statistical information. If the -n flag is set, the module will only print the legend information without drawing the map. If the user gives a legendfile, the module will write d.graph instructions for painting a legend into that file.

## EXAMPLES

### Thematic map with classes

    d.vect.thematic -l map=communes3 column=pop \
      breaks=111393.250000,222785.500000,334177.750000 \
      colors="255:0:0,0:255:0,0:0:255,0,0,0"

### Thematic map with calculated class breaks

The following example uses a calculated attribute (`density = pop/area`) and the standard deviation algorithm to calculate class breaks for 5 classes:

    d.vect.thematic -l map=communes2 column=pop/area algorithm=std \
      nbclasses=5 colors="0:0:255,50:100:255,255:100:50,255:0:0,156:0:0"

To actually draw the legend for the polygons in the graphical display, the procedure is:

    # first save legend instructions to a file
    d.vect.thematic -n map=communes2 column=pop/area algorithm=std \
      nbclasses=5 colors="0:0:255,50:100:255,255:100:50,255:0:0,156:0:0" \
      legendfile=legend_pop_dens

    # open a monitor
    d.mon wx0

    # draw the map
    d.vect.thematic map=communes2 column=pop/area algorithm=std \
      nbclasses=5 colors="0:0:255,50:100:255,255:100:50,255:0:0,156:0:0"

    # draw the legend
    d.graph input=legend_pop_dens

In order to further enhance this legend, edit the legend file accordingly and rerun the process.

### Thematic map with calculated class breaks

Example for the North Carolina sample dataset, colorizing polygons by area size:

    # first save legend instructions to a file
    d.vect.thematic -n map=geology column=SHAPE_area algorithm=int nclasses=6 \
     colors=215:48:39,252:141:89,254:224:139,217:239:139,145:207:96,26:152:80 \
     legendfile=geology.leg

    # open the graphical display
    d.mon wx0
    # draw outline of polygons
    d.vect map=geology type=boundary
    # draw color fill
    d.vect.thematic map=geology column=SHAPE_area algorithm=int nclasses=6 \
     colors="215:48:39,252:141:89,254:224:139,217:239:139,145:207:96,26:152:80" \
    # draw legend
    d.graph input=geology.leg

Thematic map of area sizes

## SEE ALSO

v.class, d.vect, d.graph, v.univar

Check also Python module from AddOns: d.vect.thematic2

## AUTHOR

Moritz Lennert

Last changed: $Date: 2015-08-11 23:07:09 +0200 (Tue, 11 Aug 2015) $