[GRASS-dev] terminology issues in grass7

[Maciej Sieczka]

Paul Kelly pisze:
> On Sun, 10 Aug 2008, Moritz Lennert wrote:

>> Well, to be absolutely precise, you don't need linked attribute tables 
>> to have multiple layers, so I'm not sure that reducing the layer 
>> concept to table links is really 100% correct.

> I think though, that connecting multiple layers to different tables is 
> the main application for layers? Are they much use for anything else? In 
> which case, calling them tables makes things clearer. Perhaps even table 
> would be enough - each vector map can be connected to multiple tables, 
> each vector map can have multiple tables, each vector map can have 
> multiple table links... is there a big difference in meaning between 
> those different sentences? I feel removing the word "link" improves the 
> clarity of the meaning without adding any additional ambiguity.

I don't agree with Paul. In GRASS vector terminology the term "table"
already has a very well defined meaning and it must not be used for
anything else.

(A "table" is an object in the database that stores the given "layer"'s
attributes, and the "table" and "layer"'s geometrical features are
linked using "key column" in which the "categories" are stored inside
the "table".)

Regarding Moritz's remark I indeed missed the fact that the vector map
having 0 or more "layers" does not directly imply it has the same number
of data "tables". Given that, "table link" to replace "layer" as I
suggested is bad. If we are to change the term, we should do it right.
How do you like "category set" then, "catset" in short? Together with
with replacing term vector "map" with vector "layer" it would yield:

Each vector "feature" (line, point etc.) can have 0 or more "categories"
in a vector "layer". Each "category" belongs to only 1 "category set".
Each "category set" of a vector "layer" can be connected or not with a
single database "table". The "key column" in that "table" stores the
"categories" of "features" present in the given "category set".

Any good?

Talking about layers (in their current meaning) - there is no convenient
tool to report the number of layers in a vector map. There is only
v.category opt=report. Could v.info be extended in this regard? Oh, and
the regular v.info already reports number of "dblinks" (which I guess
might be renamed to "table links", but I won't insist), while v.info -t
doesn't. Could this be addressed too please?

> With regard to calling maps something different though, I think that 
> would be very confusing and not a good idea (especially if they were 
> renamed to layers). Map has IMHO a much clearer meaning than layer. 
> There is the issue of ambiguity with a printed map I suppose, but use of 
> the word in that context is kind of non-technical I feel. The use of the 
> word map has a clearly defined historical meaning in GRASS (and 
> influences other words too, e.g. a mapset = a collection of maps - 
> should this be renamed a layerset?) and I feel that it should stay.

Paul has points here. Yet I *guess* I'd prefer to trade legacy for
clarity anyway. Calling GRASS "maps" "layers" would improve clarity
IMHO, especially for newcommers. Word "map" has been in use for
centuries and the word immediately brings a nice picture with north
arrow, legend and stuff to my mind. "Layer" is *the* GIS word for a set
of features that can be represented graphically as a map, as well as a
table or a set of statistic properties etc.

Maciek

-- 
Maciej Sieczka
www.sieczka.org