[GRASS-dev] v.category option=print: fails to print area's categories

Hamish hamish_nospam at yahoo.com
Sat Nov 25 02:54:43 EST 2006

Michael Barton wrote:
> A polyline with a cat value--including a closed polyline--can
> certainly be useful when it forms the boundary of an area or is in any
> other context. However, AFAICT, a "boundary" is simply a cloased
> line/arc associated with point that together define an area.

that is an "area" is simply a closed BOUNDARY line/arc associated with
CENTROID that together define an area.

the raw boundary feature type is not associated with any single point or

points,centroids are both a single point in 3D space, but are stored
differently in the vector file. Same for line,boundary. Hence v.type.

> It is nevertheless a line/arc. Adding categories to a boundary is the
> same thing as adding categories to a line/arc.

fundamentally they are both polylines. But we are abstracted from that.

> Differentiating open lines from closed ones can be useful sometimes,

boundaries can be open or closed, that has nothing to do with their
vector feature-type status.

a closed line + a centroid does not make an area. An example of a closed
line which is not a boundary is a closed contour line around a hill.

> but there is no guarantee that adding cats to boundaries will only
> affect areas, since closed lines exist with or without being
> associated with areas.

I don't understand this. Adding cats to boundaries is rare, but when it
happens it will not affect the surrounding areas one way or another.

> This can lead to confusion unless clearly explained.


> This is why I suggested dropping the boundary option; you simply
> assign cats to lines regardless of whether they border areas or not.
> If we really want to manage those lines that bound areas, then they
> need to be defined differently from closed lines that do not bound
> areas. Currently, the terminological category "boundary" includes
> both.

is this what you are asking:

v.category --help
 type   Type
           Feature type(s)
-           options: point,line,boundary,centroid,area
+           options: point,line,boundary,centroid

or this:
v.category --help
 type   Type
           Feature type(s)
-           options: point,line,boundary,centroid,area
+           options: point,line,area


I'm not sure about the first, the second is bad.


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