v.histogram

Draws the histogram of values in a vector attribute column

Command linePython (grass.script)

v.histogram map=name [layer=string] column=name [where=sql_query] plot_output=name [bins=integer] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

v.histogram map=name column=name plot_output=-

grass.script.run_command("v.histogram", map, layer="1", column, where=None, plot_output="-", bins=30, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("v.histogram", map="name", column="name", plot_output="-")

Parameters

Command linePython (grass.script)

map=name [required]
    Name of vector map
    Or data source for direct OGR access
layer=string
    Layer number or name
    Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
    Default: 1
column=name [required]
    Attribute column to create histogram from
where=sql_query
    WHERE conditions of SQL statement without 'where' keyword
    Example: income < 1000 and population >= 10000
plot_output=name [required]
    Name for graphic output file for plot (extension decides format, - for screen)
    Name for output file
    Default: -
bins=integer
    Number of bins in histogram
    Default: 30
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

map : str, required
    Name of vector map
    Or data source for direct OGR access
    Used as: input, vector, name
layer : str, optional
    Layer number or name
    Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
    Used as: input, layer
    Default: 1
column : str, required
    Attribute column to create histogram from
    Used as: input, dbcolumn, name
where : str, optional
    WHERE conditions of SQL statement without 'where' keyword
    Example: income < 1000 and population >= 10000
    Used as: input, sql_query, sql_query
plot_output : str, required
    Name for graphic output file for plot (extension decides format, - for screen)
    Name for output file
    Used as: output, file, name
    Default: -
bins : int, optional
    Number of bins in histogram
    Default: 30
overwrite: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

DESCRIPTION

v.histogram draws a histogram of the values in a vector map attribute column. Users can use the where option to only select a subset of the attribute table and can determine the number of bins (bars) used for the histogram. The plot_output parameter determines whether the result is displayed on screen (default) or exported to a graphics file.

NOTE

This is a quick and dirty solution using basic matplotlib. In future, this should be integrated into the g.gui, possibly together with the raster histogram tool.

EXAMPLE

Show the histogram of median age values in the census block map:

v.histogram map=censusblk_swwake column=MEDIAN_AGE where="TOTAL_POP>0"

Histogram of median age values in census blocks

AUTHOR

Moritz Lennert

SOURCE CODE

Available at: v.histogram source code (history)
Latest change: Thursday Feb 20 13:02:26 2025 in commit 53de819