[GRASS5] 5.7 how to merge polygons with same attribute ?

[Moritz Lennert]

Radim and Hamish,

On Mon, December 13, 2004 9:40, Radim Blazek said:
> Moritz Lennert wrote:
>> Hello,
>>
>> How do I merge polygons with the same value for a given attribute in the
>> attribute table ?
>>
>> For example: if I have a map of the world by countries, and for each country
>> an attribute "continent" in the database table with values such as "Europe",
>> "North America", etc, how could I create a map showing only the outlines of
>> the continents ?
>
> v.reclass.
>

Is there a "dissolve common boundaries" flag in v.reclass ?


On Mon, December 13, 2004 2:26, Hamish said:
>> How do I merge polygons with the same value for a given attribute in
>> the attribute table ?
>>
>> For example: if I have a map of the world by countries, and for each
>> country an attribute "continent" in the database table with values
>> such as "Europe","North America", etc, how could I create a map
>> showing only the outlines of the continents ?
>
> maybe
>
> v.extract out=eur -d where="continent='Europe'"
> v.extract out=nam -d where="continent='North America'"
> v.patch in=eur,nam

Thank you Hamish that does the trick, even though it is a bit tedious when you
have many categories...

A -d flag in v.reclass would probably be the easiest solution.

Moritz