r.statistics(1)

NAME
r.statistics

DESCRIPTION
r.statistics is a tool to analyse exploratory statistics of a "cover layer" according to how it intersects with objects in a "base layer". A variety of standard statistical measures are possible (called "zonal statistics" in some GIS). All cells in the base layer are considered one object for the analysis. For some applications, one will first want to prepare the input data so that all areas of contiguous cell category values in the base layer are uniquely identified, which can be done with r.clump.
The available methods are the following (english - german):

        distribution - Verteilung in Prozent

        average - Durchschnitt

        mode - Modalwert

        median - Median

        average deviation - Durchschnittliche Abweichung

        standard deviation - Standardabweichung

        variance - Varianz

        skewness - Schiefe der Verteilung

        kurtosis - Relative Abflachung (-) oder Zuspitzung (+)

        minimum - Minimum

        maximum - Maximum

        sum - Summe
The calculations will be performed on each area of data of the cover layers which fall within each unique value, or category, of the base layer.

Setting the -c flag the category lables of the covering raster layer will be used. This is nice to avoid the GRASS limitation to interger in raster maps because using category values floating point numbers can be stored.

All calculations except "distribution" create an output layer. The output layer is a reclassified version of the base layer with identical category values, but modified category labels - the results of the calculations are stored in the category labels of the output layer.

For distributions, the output is printed to the user interface (stdout). If an output file name was specified, it will be ignored. The result will be a text table with three columns. In the first column are the category values of the base layer (a), in the second column the associated value of the cover layers (b), and in the third column the percentage of area in that base layer category (a) that falls into that row's value in the cover layer(b). Example:
1 124 23
1 201 47
1 273 30
2 101 5
2 152 16
2 167 60
2 187 19
     .
     .
     .
So for the first line in the output above, we see that 23% of the cells of the base layer category 1 have a value of 124 in the cover layer. To transfer the values stored as category labels into cell values, r.mapcalc can be used ('@' operator).

EXAMPLES
Calculation of average elevation of each field in the Spearfish region:
r.statistics base=fields cover=elevation.dem out=elevstats method=average
r.category elevstats
r.mapcalc "fieldelev=@elevstats"
r.univar fieldelev

SEE ALSO
r.average, r.clump, r.mode, r.median, r.mapcalc, r.neighbors, r.univar r.category

AUTHOR
Martin Schroeder, Geographisches Institut Heidelberg, Germany

Last changed: $Date: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $

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