[GRASS5] Layers Clarification

[Helena Mitasova]

Radim Blazek wrote:
> On 3/8/06, Trevor Wiens <twiens at interbaun.com> wrote:
> 
>>>Yes. One geometry object can be linked to more rows in attribute table.
>>>In that case the geometry object has more categories (the same layer)
>>>each pointing to one row in the attribute table. One category can only
>>>link to one row, no more.  The relation geometry-table can be
>>>one-to-many. The relation category-table can only be
>>>on-to-one or many-to-one.
>>>
>>>It is probably much easier  get idea from a picture:
>>>   http://mpa.itc.it/radim/g51/bridge.png
>>>It covers all possible cases I think.
>>>
>>
>>Radim and others,
>>
>>Thank you for taking the time to explain this. Is it possible to
>>manually add more than one category to a geometry object or is this
>>only done through automated means such as v.clean?
> 
> 
> Yes, it is possible,
> v.digit: Display categories -> Add new
> QGIS: Edit Attributes -> New
> 
> 
>>Thanks. Once I get this all straight in my head I will assemble this
>>into a single document. Do you think my idea of having a statement on
>>the vector module index page with a link to a more detailed explanation
>>is a good idea or would somewhere else be more appropriate?
> 
> 
> I think that it could be incorporated into
> http://grass.itc.it/grass61/manuals/html61_user/vectorintro.html
> (it is currently linked from main index) but you can create
> a new document as well.

Trevor,

I think that this would be a good place where to include the layer info.
And you could also explain what the level1 and level2 means, as it comes
in error messages and v.in.ascii and v.surf.rst now allow to work with 
just level1 data. Then the sentence about v.build can be modified saying 
that v.build can also be used to build topology (level2) vector map, if
it is missing.

Thanks to all for calrifying the layers concept,

Helena

> 
> Radim
> 
> 
>>T
>>--
>>Trevor Wiens
>>twiens at interbaun.com
>>
>>The significant problems that we face cannot be solved at the same
>>level of thinking we were at when we created them.
>>(Albert Einstein)
>>
> 
> 
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