[GRASS5] Re: GRASS dissolve

Hamish hamish_nospam at yahoo.com
Wed Apr 27 18:10:25 EDT 2005

> I also just tried to do a dissolve yesterday and it didn¹t work. It
> SHOULD work using v.extract ­d. I wanted demonstrate dissolve while
> working with a student yesterday and it didn¹t work. I simply wanted
> to dissolve all the common boundaries in a map, so I didn¹t specify a
> where clause. However, nothing was dissolved. I think that it will
> only dissolve polygons with common cat value, regardless of whether or
> not you specify.

Yes, only "common" (ie redundant) boundaries separating areas of common
category are disolved.

There are several strategies for removing cats from a vector map. After
that 'v.extract -d' should do what you want it to. Luckily it is easier
to remove cats then to add them, e.g. make a new column with common cat
numbers and run 'v.reclass column=' or try 'v.category option=del' + 
'v.category option=add cat=1 step=0'.


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