[GRASSLIST:9440] Re: v.extract and vector table

[Radim Blazek]

Until somebody adds -d to v.reclass you have to do it in 2 steps:

v.reclass (to get the same cat for areas you want to merge)
v.extract (to dissolve common boundaries)

Radim

On 12/13/05, Nick Cahill <ndcahill at facstaff.wisc.edu> wrote:
> I'm trying to dissolve the boundaries between adjacent areas which
> have common attributes in their vector database. I understand that
> the best tool for this is v.extract. The maps are derived from vmap0
> political boundary coverages; the problem with these is that the maps
> were tiled, so regions span across adjacent ex-tiles, with the same
> names and other attributes. I'd like to end up with a single area and
> centroid for each region, with the original database attributes.
>
> As a test I tried it with one regional unit, BURDUR. If I run
>
> v.extract input=polbndr output=burdur
> type=point,line,boundary,centroid,area,face layer=1 new=-1
> where=a_nam='BURDUR' -d
>
> with new=-1, it doesn't merge the two areas because the category
> values are different in the two areas. So I try assigning a new
> category:
>
> v.extract input=polbndr output=burdur2
> type=point,line,boundary,centroid,area,face layer=1 new=500
> where=a_nam='BURDUR' -d
>
> This merges the vectors properly, but this doesn't seem to create a
> new table for the newly created vector. The centroid has the proper
> category, but there is no table associated. Do I have to create a new
> table by hand and then link the vector to this table? Or is there an
> easier way to do this? I don't look forward to doing each
> administrative unit which spans different tiles on these vmap0 maps.
>
> Any help would be gratefully appreciated.
>
> Nick Cahill
>
>