[GRASS-user] grass vector model, cats and layers concept

Benjamin Ducke benducke at fastmail.fm
Mon Apr 22 11:23:54 PDT 2013

On 04/22/2013 04:38 PM, Vincent Bain wrote:
> Le lundi 22 avril 2013 à 14:58 +0200, Moritz Lennert a écrit :
>> On 22/04/13 14:41, Vincent Bain wrote:
>>> Thank you Moritz,
>>>> - I'm not sure I like the difference in size of cat values between
>>>> layers. It gives the idea that there is one important and two secondary
>>>> layers.
>>> Sorry, I don't understand. Cats values are all the same font size in the
>>> drawing (I turned "1" values to sth else, perhaps an optical illusion)
>> Sorry, I was confused by your "id". I'm not sure that this id is helpful
>> in your drawing as most users will never be confronted to id's, only to
>> cat values. I think making them this prominent in the drawing might
>> cause more confusion than help in understanding.
> I agree with you that most users won't feel concerned by the feature-id,
> especially the majority of people working on imported data (what's more
> for the user, there's no way to manage this internal numbering). Those
> who learn grass in order to /produce/ geographical data may very soon in
> their learning process be concerned by this. My humble opinion is that
> awareness of the existence of a geometrical identifier is an integral
> part of the problem. I would keep it in the sketch, perhaps as you
> suggest in a less prominent appearance.

+1. Like so many, I also got confused about this
the first time I started working with the GRASS
vector API.

Maybe you could put a short note somewhere on the
illustration stating that "the internal feature ID
is assigned automatically and can be used to select
geometries directly (using v.edit)"
or similar.



>> No, what I meant is to have a unique cat for each plot in layer 2 and
>> then have an attibute table with columns cat and type, the second then
>> giving the type of the plot, while the first is a unique identifier of
>> each plot.
> OK, I'll have a look.
> Thanks,
> V.
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Dr. Benjamin Ducke, M.A.
{*} Geospatial Consultant
{*} GIS Developer

   benducke at fastmail.fm

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