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

Michael Barton michael.barton at asu.edu
Wed Nov 22 21:00:29 EST 2006

I'd suggest removing centroid AND boundary from the type list and explaining
the centroid+boundary=area relationship in the docs. Lines can have
categories, but it makes no sense for a "boundary" to have a cat if it is
really the boundary of an area. If it is not, it is simply a closed

The underlying topology of GRASS vectors is logical and sensible overall.
However, the terminology is a legacy that should be discussed as such, but
it should not confront the everyday user.

Functionally, GRASS is like any other vector GIS in that is has points,
lines/arcs, and polygons/areas. This is how it should be presented to the
normal user. 

The fact that a polygon/area is built from a closed line/arc and an
associated point that is located inside the closed line/arc seems to be a
very clean kind of underlying organization. It makes it nice to teach about
GIS and geospatial data. It also makes manipulating those data in
sophisticated ways more transparent. BUT the normal user doesn't really need
to know that simply to do basic GIS activities.

So my recommendation is to explain this in the docs so that users can learn
sophisticated techniques like reassociating sets of boundaries and points to
create areas with new kinds of data. In this respect, we should also leave
this in v.type for vector type conversions (though this module needs to have
a better GUI and explanations to be usable). However, we should drop
references to centroids and boundaries in most other places--like in
v.category or d.vect. Somehow, we also need to make vectors respond to mouse
clicks anywhere inside their boundaries and not just on the centroid. GRASS
is complex enough without including options and terminology that don't
really offer anything to users.

My 2 cents worth

Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

> From: Moritz Lennert <mlennert at club.worldonline.be>
> Date: Wed, 22 Nov 2006 14:30:34 +0100
> To: Martin Landa <landa.martin at gmail.com>
> Cc: grass-dev <grass-dev at grass.itc.it>
> Subject: Re: [GRASS-dev] v.category option=print: fails to print area's
> categories
> Martin Landa wrote:
>> Hi,
>> 2006/11/22, Moritz Lennert <mlennert at club.worldonline.be>:
>>> I'd rather suggest to map area to centroid (i.e. if area is given behave
>>> the same as if centroid is given), as intuitively people are looking for
>>> information concerning areas not centroids.
>> Area = centroid + boundary
>> simplification you suggest tend to be misguided;-) I prefer (but not
>> sure) removing area from the type list and update manual pages of
>> v.category to make it clear to user. What do you think about it?
> I think both approaches are valid. My suggestion tries to just gloss
> over the user's lack of understanding, yours tries to teach him. So
> probably yours is better and more in line with the general GRASS approach.
> Moritz

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