[GRASSLIST:4916] Re: [GRASS5] field -> layer

[Radim Blazek]

5.7 vectors: options 'field' were changed to 'layer'

Related:
v.category: option=chfield -> option=chlayer
v.out.ogr: layer -> olayer

Radim

Radim Blazek wrote:
> Michael Barton wrote:
> 
>> Radim,
>>
>> I'm glad you brought this up. It took me awhile to even figure out what
>> "field" meant, given my long association with databases. I agree that the
>> name should be changed. But let me ask to make sure exactly how 'field'
>> works to make sure I do understand it correctly now.
>>
>> A set of vectors (i.e., shapes in a single vector map) can be associated
>> with more than one attribute table. 'Field' makes the connection 
>> between the
>> vectors and each of the the attribute tables. Field1 connects to the 
>> default
>> table, while field2, field3... connect the same vectors to other tables.
>>
>> If this is correct, I suggest using the term connection or link rather 
>> than
>> layers. Layer can often imply a different set of vector shapes.
>>
>> However, if I still don't understand how this works I hope you can set me
>> straight.
> 
> 
> It is possible to link one geometry to more tables, it is not
> the typical case however. Usually, if more fields are used,
> the different elements are linked to different tables.
> For example, if a landcover map contains forests, lakes and
> fields, each centroid is linked only to one table,
> using one link. The tables have different structure.
> That vector in GRASS is equivalent to for example 3 shapefiles,
> 3 layers: forests, lakes, field.
> Export to simple feature results in 3 layers.
> In QGIS (simple feature model), all GRASS features with the
> same field are put to one layer.
> 
> The name link is not appropriate, because the field can be
> a link, but it can be also used in the vector, but there
> are no connected tables.
> 
> Have you evere played with?: 
> http://mpa.itc.it/radim/g51/g51test-12-multi.tar.gz
> 
> Radim
> 
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