d.vect.thematic(1)

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 further 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 basin polygons by average elevation:

# create watersheds from elevation map
r.watershed elevation=elevation threshold=10000 basin=basins_10k
# convert raster to vector
r.to.vect input=basins_10k output=basins_10k type=area column=basin_num
# upload raster statistics to each polygon in vector map
v.rast.stats map=basins_10k raster=elevation column_prefix=elev_
# save legend instructions to a file
d.vect.thematic -n map=basins_10k column=elev_average algorithm=int \
  nclasses=5 colors=228:26:28,55:126:184,77:175:74,152:78:163,255:127:0 \
  legendfile=d_vect_thematic_leg.txt
# open a graphical display
d.mon wx0
# draw outline of polygons
d.vect map=basins_10k type=boundary
# draw color fill
d.vect.thematic map=basins_10k column=elev_average algorithm=int \
  nclasses=5 colors=228:26:28,55:126:184,77:175:74,152:78:163,255:127:0
# set a different font (list fonts with: d.font -l)
export GRASS_FONT="sans"
# and finally draw legend, but edit the legend file first (for example:
# set size to 20, remove feature counts and most decimal digits)
d.graph input=d_vect_thematic_leg.txt

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: 2016-07-06 22:51:29 +0200 (Wed, 06 Jul 2016) $

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