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

[Hamish]

> 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

?

for a larger number of items (eg country='Grand Fenwick') I guess you'd
need a script containing a loop.


Hamish