[GRASS-dev] terminology issues in grass7

[Markus GRASS]

Maciej Sieczka wrote:
> Markus GRASS pisze:
>> Hamish wrote:
>
>>> (if it must be renamed, what's was wrong with going back to
>>> "field"?) [I remember Radim explained on-list why that was changed
>>>  when it became "layer", ... need to dig out that thread]
>
>> Here are two interesting threads [1,2], the same discussion about
>> field/layer between Trevor Wiens, Radim Blazek, Michael Barton, and
>> Moritz Lennert in March 2006:
>>
>> [1] http://lists.osgeo.org/pipermail/grass-dev/2006-March/021646.html
>>  and responses [2]
>> http://lists.osgeo.org/pipermail/grass-dev/2006-March/021659.html and
>>  responses
>>
>> Maybe layer is not that bad after all... GRASS can import several OGR
>>  layers into one vector, each OGR layer will become a separate GRASS
>> vector layer. The main difference to e.g. several shapefiles imported
>> as different layers into one GRASS vector is that GRASS builds and
>> maintains topology for all geometry objects in all shapefiles
>> combined.
>
>> OGR layers and GRASS vector layers are not a 100% match, but IMHO
>> pretty close.
>
> IMHO they are not close enough to call them the same name. 
At least OGR calls them layers [e.g. 1, 2].
> GRASS
> vector layers most of the time have common geometry or "subject", OGR
> layers not necessarily. E.g. shapefiles in a directory don't need to
> have anything in common. 
Same for GRASS vector layers, as long as it's in the same projection and
topology does not interfere. Technically speaking, even two polygons in
the same shapefile have nothing in common because there is no topology
and they can not relate to the same entry in an attribute table.
> They are just stored in the same place. 
You could call that messy data management if data that have nothing in
common are stored in the same place, no offence;-) Just because it's
technically possible doesn't mean that it makes sense, and GRASS is
discouraging this although it is to a degree possible. Usually, when I
get a directory with shapefiles, they are indeed related to each other,
and if possible I import all of them into one vector as different layers.

Markus M

[1] http://www.gdal.org/ogr/drv_grass.html
[2] http://www.gdal.org/ogr/drv_shapefile.html