[GRASS-user] Two questions - vector data and Mac install

[Moritz Lennert]

On 26/06/08 08:49, Richard Chirgwin wrote:
> Moritz Lennert wrote:
>> On 25/06/08 02:46, Richard Chirgwin wrote:
>>> Hi all,
>>>
>>> 1) v.overlay question
>>>
>>> I have three maps: two area vectors (A and B), and a v.overlay result 
>>> (C). Is there a simple way to assign the percentage of areas in (A) 
>>> covered by the overlay (C)?
>>
>> Vector solution:
>>
>> http://lists.osgeo.org/pipermail/grass-user/2008-June/045290.html
>>
>> Moritz
>>
> Moritz,
> 
> This led me straight into an oddity. One of my vectors is created by 
> buffering around points.
> 
> The source map was a set of 800 points. V.buffer runs successfully, and 
> when it ends, the new areas display without problem. However, when I run 
> v.db.addtable, there are only 18 categories - any ideas?

As GRASS is topologically clean, areas cannot overlap. v.buffer, 
therefore, fusions those buffers that do. So if your 800 points are 
close enough to each other to make the buffers overlap, they might 
result in only 18 distinct polygons. This should be visible when you 
display them.

Moritz