[GRASS-dev] future thematic cartography in GRASS

[Michael Barton]

On Mar 4, 2010, at 10:00 AM, grass-dev-request at lists.osgeo.org wrote:

> Date: Thu, 04 Mar 2010 11:26:48 +0100
> From: Moritz Lennert <mlennert at club.worldonline.be>
> Subject: Re: [GRASS-dev] future thematic cartography in GRASS [was:
>        Re: [GRASS      GIS] #974: [Patch] add option to d.vect to make symbol size
>        proportionate to square root of size_column]
> To: Hamish <hamish_b at yahoo.com>
> Cc: grass-dev at lists.osgeo.org
> Message-ID: <4B8F8AE8.3050803 at club.worldonline.be>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 03/03/10 11:44, Hamish wrote:
>>> However, if we go this way, I would need to add a flag to
>>> d.vect which allows sorting symbols with the largest in the
>>> back. This is absolutely necessary for readability. However,
>>> this implies a fundamental change in the d.vect code,
>> 
>> As this is just the beginning, I would prefer a new module for that
>> along the lines of d.vect.chart.
> 
> Ok, I'll go in this direction then.
> 
>> why not simplify the name to just "d.thematic"?
> 
> The idea was to simplify modules and so to separate areas from symbols
> (incl. lines), but it is obviously possible to put everything together
> into one module.
> 
>> ps- see also v.colors and the new extra/ring symbol
> 
> Yeah, we could include discrete color schemes in v.colors by feeding it
> class breaks.
> 
> So in summary this means as tasks at hand:
> 
> - write an alternative d.vect with attribute-based selection, allowing
> sorting of symbols largest in the back
> 
> - enhance v.colors to provide discrete color schemes (possibly including
> the color brewer schemes which are licensed under the Apache license)
> 
> - write a script which combines the existing tools (v.class, v.colors,
> d.vect / d.vect2) to allow for thematic cartography
> 
> - write a module/script which displays thematic legends (color classes
> and sizes)
> 
> This would make d.thematic.area obsolete.
> 
> As mentioned, my time is limited and I don't know how quickly I could do
> all this. If anyone's interested in helping, this would be great.
> 
> Moritz

This sounds very good. FWIW, my vote is to NOT patch this together with scripts but create a comprehensive d.thematic module with these capabilities--except legend. A single module would work much better across multiple platforms and be a snap to implement in the GUI or on the command line (wximgview). If a d.thematic gets created, we should take out the thematic mapping components of d.vect to simplify this very complex module. Finally, if there is some way to enhance d.legend to work with thematic vector maps as well as raster maps, it would be desirable.

Michael