d.vect.thematicgrass - Online in the Cloud

PROGRAM:

NAME

d.vect.thematic - Displays a thematic vector map in the active graphics frame.

KEYWORDS

display, cartography, choropleth map, legend

SYNOPSIS

d.vect.thematic
d.vect.thematic --help
d.vect.thematic [-len] map=name [layer=string] column=name [breaks=string[,string,...]]
[algorithm=string] [nclasses=integer] colors=string[,string,...] [where=sql_query]
[boundary_width=integer] [boundary_color=name] [legendfile=name] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]

Flags:
-l
Create legend information and send to stdout

-e
When printing legend info, include extended statistical info from classification
algorithm

-n
Do not draw map, only output the legend

--overwrite
Allow output files to overwrite existing files

--help
Print usage summary

--verbose
Verbose module output

--quiet
Quiet module output

--ui
Force launching GUI dialog

Parameters:
map=name [required]
Name of vector map
Or data source for direct OGR access

layer=string
Layer number or name
Layer number. If -1, all layers are displayed.
Default: 1

column=name [required]
Name of attribute column to be classified

breaks=string[,string,...]
Class breaks, without minimum and maximum

algorithm=string
Algorithm to use for classification
Options: int, std, qua, equ, dis
int: simple intervals
std: standard deviations
qua: quantiles
equ: equiprobable (normal distribution)

nclasses=integer
Number of classes to define

colors=string[,string,...] [required]
Colors (one per class)

where=sql_query
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and inhab >= 10000

boundary_width=integer
Boundary width
Default: 0

boundary_color=name
Boundary color
Either a standard color name or R:G:B triplet
Default: black

legendfile=name
File in which to save d.graph instructions for legend display

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

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