[GRASS-dev] Re: terminology issues in grass7

[Michael Barton]

On Jun 16, 2009, at 12:39 PM, Paul Kelly wrote:

> On Tue, 16 Jun 2009, Michael Barton wrote:
>
>> In GRASS, displaying Layer 1 will show all objects for some vector
>> topologies, and only ID 1 and 2 for other topologies. However, by  
>> putting
>> values into cat for Layer 1, you can also display ID's 3 & 4 for  
>> Layer 1. You
>> can achieve the same effect by querying cat = 1 for Layer 2. The  
>> difference
>> is that sometimes empty cats are displayed and sometimes they are  
>> not. To me
>> this is kind of an automatic (inadvertent even) query. Some of this  
>> is only
>> semantics, but I think we all agree that semantics can be important.
>
> IMHO these are all side-effects of the inconsistent way layers are  
> handled
> amongst different GRASS modules. It's an implementation problem  
> (perhaps
> caused by confusion among developers as options were added and  
> modified
> over the years), rather than a fundamental problem with the layer  
> concept.

The inconsistent implementation is an issue certainly. I don't think  
that there is a problem with underlying concept of the layer feature.  
Indeed, it is a very powerful data management feature of GRASS. I just  
think that another name for the feature would help users to understand  
and make use of it better--especially since we also use the term  
layers in the GUI layer manager to refer to superimposed displays of  
distinct geospatial data files, a very common usage in GIS.

>
> If we manage to come to a full understanding of the capabilities and
> possibilities of the concept of vector layers in GRASS (which I feel  
> this
> discussion is really helping us to work towards, for me anyway),  
> then it
> would be an exciting project to do an audit of all vector modules  
> and the
> way they handle layers, and tidy up all the inconsistencies so that  
> the
> meaning of layers is much more obvious, simply from the module  
> options and
> flags. Perhaps too radical though.
>
> Paul

I agree 100%.

Michael