[GRASS5] One more thing related to layers

[Trevor Wiens]

I'm starting to think about who to update the layers documentation. I
know that every geometry object within in one layer can have one or
more categories. Can it also have none? To use the forest / lake
example. Is it possible to have a lake virtual layer in which only
lakes will appear and forest virtual layer in which only forests
appear? AFAICT this would require having some geometry objects having
no CAT values in the corresponding layers where they shouldn't be
visible. Is this correct?

T
-- 
Trevor Wiens 
twiens at interbaun.com

The significant problems that we face cannot be solved at the same 
level of thinking we were at when we created them. 
(Albert Einstein)