[GRASS-dev] Areas

[Hamish]

> When starting to think about areas I played with v.digit a bit, and
> it seems that it creates different cat for the boundary and centroid.

Any feature has the ability to have a cat assigned to it (v.category
type=). That doesn't mean it _should_ have a cat assigned to it for
normal use.

> Is this what we want? I've always thought of them as kind of bound
> together, and thus would expect them to have the same cat.

boundaries typically won't have a cat number. An area takes on the
attributes of the centroid within it (which floats in the same space).
The boundary is just the boundary, the example was given of a boundary
that borders two areas - it's ambiguous to assign it to a given cat.
(but see "v.to.db option=sides" if you must)

> Am I totally off base here? What about islands? Should they have a cat
> at all,

no, they are "outside" or "not of" the main area. 
It may be better to think of islands as holes in the area.

> or should they have the same cat as the area that they belong to?

no, then they would be the same as the area. Think of labled "fields".

> Or something totally different?

for most use the boundary is without cat, the islands/holes are without
centoriod (and thus no cat), and only the centroid provides cat and
attribute values for the surrounding area. AFAIU, "area" is a virtual
feature.


Hamish