[GRASS-user] update cat column in vector data set

[Markus Metz]

On Thu, Aug 16, 2012 at 1:10 PM, Stefan Luedtke <sluedtke at gfz-potsdam.de> wrote:
> Dear friends,
>
> I am struggling with the following point.
>
> I have created a shape of subbasins based on a raster data set. Since this
> yields some tiny (pixel size) areas, I run "v.clean" with a certain
> threshold to remove/append those artifacts. However, the resulting vector
> data set still holds all categories of the old one, even so, some areas have
> been removed.

This is because several areas can belong to the same category, e.g.
basin id, and the category of a deleted area may still be used by
another, existing area. BTW, it is not uncommon that one raster basin
is represented by several vector areas.
>
> So my question: How can I update these values that the number of categories
> matches the number of areas?

You can delete the table and create a new table. Otherwise, entries in
the attribute table that are no longer used do not do harm.

HTH,

Markus M

>
> I tried v.category (but der is not update function).
>
> Cheers,
>
> Stefan
>
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