## DESCRIPTION

In GRASS GIS, a centroid is a point within a closed ring of boundaries. A vector area is defined as composite entity consisting of a set of closed boundaries and a centroid. The attribute information associated with this area is linked to the centroid. The v.centroids module adds centroids to closed boundaries in the input file and assigns a category number to them. The starting value as well as the increment size may be set using optional parameters.

Multiple attributes may be linked to a single vector entity through numbered fields referred to as layers. Refer to v.category for more details, as v.centroids is simply a frontend to that module.

The boundary itself is often stored without any category reference as it can mark the border between two adjacent areas. Thus it would be ambiguous as to which feature the attribute would belong. In some cases it may, for example, represent a road between two parcels of land. In this case it is entirely appropriate for the boundary to contain category information.

## EXAMPLES

Create an area from a closed line using North Carolina sample dataset:

    v.type input=busroute11 output=busroute11_boundary from_type=line to_type=boundary
    v.centroids input=busroute11_boundary output=busroute11_area

Figure: Creating area from closed line

## SEE ALSO

v.category

## AUTHORS

module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
help page: Trevor Wiens