[GRASS-user] RE: Problem querying layers other than '1' in gi s.m

[Radim Blazek]

On 9/22/06, Moritz Lennert <mlennert at club.worldonline.be> wrote:
> You can actually assign several category values to one object within the
> same layer. I don't really see the use of that (but I imagine there is one).

There are more, examples:
- Overlapping areas, e.g. a road on a bridge and a road below
- Many records with different time for the same point

> It would be interesting to hear how many people actually use layers and
> how they use them. I personally don't use them at all, as I normally
> don't mix different types of objects in the same map. Maybe others could
> give some use cases.

An example from my last project are targets of bombing (WWII)
where each target (can be point, line or area) has many attacks
(dates differ) in one layer (table) and summary table (bombs/target)
is linked to the second layer.  Here you have both mix of types
and layers.

Radim