[GRASS-user] grass vector model, cats and layers concept

[Nikos Alexandris]

Nikos Alexandris:

> > Still, I find it counter-intuitive that it's required to create a new
> > vector map to achieve that.
> > 
> > --%<---
> > v.category in=wrs2_tiles_of_interest_testing at PERMANENT layer=2 option=add
> > 
> > ERROR: Output vector wasn't entered
> > --->%--

Markus Metz wrote:
 
> Because you need to modify vector geometries in order to add a new
> layer. Categories and layers are first and foremost stored together
> with the geometries. Whenever geometries are modified, the result will
> be a new vector map (with the exception of v.edit and the digitizers).

Just for (even more) completeness and understanding:  adding a new layer does 
not really change the geometries per-se (that is the topology, the shape).  
It's the inner design of the vector data model, i.e. the fact that categories 
and layers are bound together.

Is it wrong to describe it as an internal "indexing" issue or similar?

Thanks, N