[GRASS-user] Question about layers and categories

[Moritz Lennert]

On 05/04/13 12:03, Vincent Bain wrote:
> Hello Mortiz,
> your reply helped me much. Removing/Reassigning layers is a matter of
> several steps :
> -drop previous layer definition, optionally drop related table;

Please note: as MarkusM has already mentioned, you cannot drop a "layer 
definition". You can drop the definition of a connection of a given 
layer in a vector map to an attribute table. Whether or not a given 
layer "exists" only depends on whether there are category values defined 
for that layer for at least one feature in the map.

Have you read "Vector object categories and attribute management" -> 
"layers" on [1]. If not please do so and tell us if we can improve the 
explanation.



[1] http://grass.osgeo.org/grass64/manuals/vectorintro.html


> -delete unused layer categories;

This is probably the closest you can get to "deleting a layer".

> -change remaining categories layer assignment (it is the step I
> misunderstood till then );
> -define new layer.
>
> This operation is perhaps not so "exotic" considering the wxGUI update
> attribute issue.

[...]

>
>>
>> Which version of GRASS are you working in ?
>
> GRASS version:
> 6.4.3svn
> GRASS SVN Revision:
> 55280

Then you should at least be able to query vector maps with several 
layers and get a result in the command console. You do not get the 
update dialog, though. Something to be worked on for grass7 I think.

Moritz