Provided by: grass-doc_7.6.0-1_all

**NAME**

v.qcount- Indices for quadrat counts of vector point lists.

**KEYWORDS**

vector, statistics, point pattern

**SYNOPSIS**

v.qcountv.qcount--helpv.qcount[-g]input=name[layer=string] [output=name]nquadrats=integerradius=float[--overwrite] [--help] [--verbose] [--quiet] [--ui]Flags:-gPrint results in shell script style--overwriteAllow output files to overwrite existing files--helpPrint usage summary--verboseVerbose module output--quietQuiet module output--uiForce launching GUI dialogParameters:input=name[required]Name of input vector map Or data source for direct OGR accesslayer=stringLayer number or name (’-1’ for all layers) A single vector map can be connected to multiple database tables. This number determines which table to use. When used with direct OGR access this is the layer name. Default:-1output=nameName for output quadrat centers map (number of points is written as category)nquadrats=integer[required]Number of quadratsradius=float[required]Quadrat radius

**DESCRIPTION**

v.qcountcomputes six different quadrat count statistics that provide a measure of how much an user defined point pattern departs from a complete spatial random point pattern. Points are distributed following a complete spatial randomness (CSR) pattern if events are equally likely to occur anywhere within an area. There are two types departure from a CSR: regularity and clustering. Figure 1 gives an example of a complete random, regular and a clustered pattern.Figure1:Realizationoftwo-dimensionalPoissonprocessesof50pointsontheunitsquareexhibiting(a)completespatialrandomness,(b)regularity,and(c)clustering.Various indices and statistics measure departure from CSR. Thev.qcountfunction implements six differentquadratcountindices that are described in Cressie (1991; p. 590-591)[1] and in Ripley (1981; p. 102-106)[2] and summarized in Table 1.Table1:IndicesforQuadratCountData.AdaptedfromCressie[1],thistableshowsthestatisticscomputedforthequadratsinFigure2.These indices are computed as follows:v.qcountchoosesnquadradscircular quadrats of radiusradiussuch that they are completely within the bounds of the current region and no two quadrats overlap. The number of points falling within each quadrat are counted and indices are calculated to estimate the departure of point locations from complete spatial randomness. This is illustrated in Figure 2.Figure2:Randomlyplacedquadrats(n=100)with584samplepoints.The number of points is written as category to theoutputmap (and not to an attribute table).

**NOTES**

This program may not work properly with lat-long data. It useshypot()in two files:count.candfindquads.c.

**SEE** **ALSO**

v.random,v.distance,v.neighbors,v.perturb

**REFERENCES**

Generalreferencesinclude:[1] Noel A. C. Cressie.StatisticsforSpatialData. Wiley Series in Probability and Mathematical Statistics. John Wiley & Sons, New York, NY, 1st edition, 1991. [2] Brian D. Ripley.SpatialStatistics. John Wiley \& Sons, New York, NY, 1981.Referencestotheindicesinclude:[3] R. A. Fisher, H. G. Thornton, and W. A. Mackenzie. The accuracy of the plating method of estimating the density of bacterial populations.AnnalsofAppliedBiology, 9:325-359, 1922. [4] F. N. David and P. G. Moore. Notes on contagious distributions in plant populations.AnnalsofBotany, 18:47-53, 1954. [5] J. B. Douglas. Clustering and aggregation.SankhyaB, 37:398-417, 1975. [6] M. Lloyd. Mean crowding.JournalofAnimalEcology, 36:1-30, 1967. [7] M. Morista. Measuring the dispersion and analysis of distribution patterns.MemoiresoftheFacultyofScience,KyushuUniversity,SeriesE.Biology, 2:215-235, 1959.Amoredetailedbackgroundisgiveninthetutorial:[8] James Darrell McCauley 1993. Complete Spatial Randomness and Quadrat Methods - GRASS Tutorial on v.qcount

**KNOWN** **ISSUES**

Timestamp not working for header part of counts output. (2000-10-28)

**AUTHORS**

James Darrell McCauley when he was at: Agricultural Engineering Purdue University Modified for GRASS 5.0 by Eric G. Miller (2000-10-28) Modified for GRASS 5.7 by R. Blazek (2004-10-14)Lastchanged:$Date:2018-09-3018:55:29+0200(Sun,30Sep2018)$

**SOURCE** **CODE**

Available at: v.qcount source code (history) Main index | Vector index | Topics index | Keywords index | Graphical index | Full index © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual