**-g**- Print results in shell script style
**--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

**input**=*name***[required]**- Name of input vector map
- Or data source for direct OGR access
**layer**=*string*- Layer 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:
*-1* **output**=*name*- Name for output quadrat centers map (number of points is written as category)
**nquadrats**=*integer***[required]**- Number of quadrats
**radius**=*float***[required]**- Quadrat radius

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.

Various indices and statistics measure departure from CSR. The
*v.qcount* function implements six different *quadrat count*
indices that are described in Cressie (1991; p. 590-591)[1] and in Ripley (1981;
p. 102-106)[2] and summarized in Table 1.

These indices are computed as follows: *v.qcount* chooses
**nquadrads** circular quadrats of radius **radius** such 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.

The number of points is written as category to the **output** map (and not
to an attribute table).

[1] Noel A. C. Cressie. *Statistics for Spatial Data*.
Wiley Series in Probability and Mathematical Statistics. John Wiley
& Sons, New York, NY, 1st edition, 1991.

[2] Brian D. Ripley. *Spatial Statistics*.
John Wiley \& Sons, New York, NY, 1981.

**References to the indices include:**

[3] R. A. Fisher, H. G. Thornton, and W. A. Mackenzie.
The accuracy of the plating method of estimating the density of
bacterial populations.
*Annals of Applied Biology*, 9:325-359, 1922.

[4] F. N. David and P. G. Moore. Notes on contagious distributions in
plant populations. *Annals of Botany*, 18:47-53, 1954.

[5] J. B. Douglas. Clustering and aggregation.
*Sankhya B*, 37:398-417, 1975.

[6] M. Lloyd. Mean crowding.
*Journal of Animal Ecology*, 36:1-30, 1967.

[7] M. Morista. Measuring the dispersion and analysis of distribution
patterns. *Memoires of the Faculty of Science, Kyushu University, Series E.
Biology*, 2:215-235, 1959.

**A more detailed background is given in the tutorial:**

[8] James Darrell McCauley 1993. Complete Spatial Randomness and Quadrat Methods - GRASS Tutorial on v.qcount

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)

Available at: v.qcount source code (history)

Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

© 2003-2021 GRASS Development Team, GRASS GIS 7.9.dev Reference Manual