[GRASS-user] Query: number of 'areas' reported in v.build output does not necessarily represent different geographical areas

[RichardC]

Hi,

Would my understanding be correct in that a given 'geographical area'
displayed in the Map Display could be counted as multiple 'areas' in the
v.build console output due to multiple centroids being associated with the
given area.

For instance, I imported a vector shapefile with the following topology:

Number of nodes: 1001
Number of primitives: 1322
Number of points: 0
Number of lines: 0
Number of boundaries: 1088
Number of centroids: 234
Number of areas: 323
Number of isles: 2
Number of duplicate centroids: 13
Number of areas without centroid: 102

With closer inspection of the displayed file, there are clearly 10
delineated areas, certainly not 323. The majority of centroids seem to sit
on boundary lines.

It appears that each 'area' counted in the v.build output represents a
single centroid AND a closed ring of boundaries* where an actual
geographical area can be counted multiple times due to multiple centroids
sitting on its boundaries. In other words, the number of 'areas' in v.build
output does not necessarily represent different geographical areas?

Thanks for your feedback.

Richard


*According to the GRASS vector introduction, an area is described as 'the
topological composition of a closed ring of boundaries and optionally a
centroid'.
http://grass.osgeo.org/grass64/manuals/vectorintro.html








--
View this message in context: http://osgeo-org.1560.x6.nabble.com/Query-number-of-areas-reported-in-v-build-output-does-not-necessarily-represent-different-geographics-tp5052007.html
Sent from the Grass - Users mailing list archive at Nabble.com.