[GRASS-user] survey: use of different geometry types in same vector map

[Markus Metz]

On Wed, Mar 5, 2014 at 12:08 PM, Moritz Lennert
<mlennert at club.worldonline.be> wrote:
> Hello,
>
> Recent discussions here with colleagues about GRASS' vector format and the
> teaching of vector handling in GIS have brought up a question about the fact
> that GRASS (contrary to some other well-known vector formats) allows a mix
> of geometry types (points, lines, polygons) in the same map, something which
> some GIS'ers consider quite unorthodox.

Nothing to add to Ben's reply from a user perspective.

>From a conceptual perspective, it depends on the definition of "vector
map". Considering the number of vector formats (76 supported by OGR),
any definition must be independent of a specific vector format.

In OGR, a vector is defined as a data source which contains any number
of layers which in turn contain vector geometry objects. A vector
geometry object in turn can be a collection of vector geometry objects
of possibly different types. This property of a geometry object and
geometry collection conforms to the OGC simple feature specification,
a software and vector format independent (!) standard. That means that
even a single geometry object in a single layer in a single data
source can contain multiple feature types.

In my experience, a common task (probably the most common task) is to
convert GIS data of any format to the format of your choice. Thus I
would be surprised if regular GIS users are not familiar with the
diversity you find out there in the wild.

Markus M

>
> In order to enrich the reflection on that, I would like to ask GRASS users
> for use cases where this mix has been useful. Do you use such mixed geometry
> maps ? Which specific use cases do you use them for ?
>
> In order not to flood the mailing list, you can also send me your response
> by private mail. I'll report back to the mailing list with the results.
>
> Moritz
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user