[GRASS-user] Vector Overlay Issues

[Michael Barton]

On Feb 13, 2008, at 11:50 PM, grass-user-request at lists.osgeo.org wrote:

> Date: Wed, 13 Feb 2008 12:21:34 -0700
> From: Eddie <eddie at mailforce.net>
> Subject: Re: [GRASS-user] Vector Overlay Issues
> To: grass-user at lists.osgeo.org
> Message-ID: <1202930494.8372.4.camel at localhost>
> Content-Type: text/plain
>
> Someone sent me an E-mail regarding my use of HTML in the previous
> message and I'm sorry about that. Always learning. Allow me to re- 
> phrase
> in plain text.
>
> I have been struggling for quite some time trying to make a land use
> vector map out of two separate vector maps. One is water and the other
> is vegetation. Both only contain areas, and those areas which are  
> active
> are set to a single category value (1 for water, 2 for vegetation).
> Islands are valid areas with no category id. I have tried the  
> following
> two approaches
>
> v.patch input=water,vegetation out=landuse
> v.overlay ainput=water atype=area binput=vegetation btype=area
> output=landuse operator=or
>
> to no avail. The results is always something bizarre that I haven't
> quite figured out the meaning of. Certainly not what one would expect.
> Both maps appear to be topographically correct. I have uploaded a
> tar.bz2 of the project file at
> (http://eddie.alcazarmountain.com/kootenay.tar.bz2). I removed all the
> other map files leaving only the two vector maps and a region setting.
> It is only about two megabytes. I am running {GRASS 6.2.1 (2006)} on
> {Linux spica 2.6.23-gentoo-r6 #1 Mon Jan 28 11:06:48 MST 2008 x86_64
> Mobile AMD Athlon(tm) 64 Processor 3000+ AuthenticAMD GNU/Linux}.

I'm not positive what kind of output you are hoping for, but it  
sounds like you should be using the *and* operator instead of the  
*or* operator. "And" does an intersection (normally what you want for  
a model like you describe), and "or" does a union.

Michael