[GRASS-user] displaying many thematic maps from one vector dataset

[Vishal Mehta]

Hi Moritz, all,

In displaying this kind thematic vector data, how can I assign a transparent
color to the value zero? (zero is Not the null value of the GRASS vector
dataset)

Thanks,
Vishal

On Wed, Apr 8, 2009 at 10:24 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

> On 08/04/09 18:48, Vishal Mehta wrote:
>
>> Hi Moritz,
>> Regarding legends with d.graph, these are the main issues where I found I
>> needed to do too much of trial and error, some of which I think could
>> probably be avoided/improved in a future version...
>>
>> 1. the legend ends up with some strange additions beyond just the range of
>> data: like what are those numbers after each range
>> e.g. in the example below where did | 0 and | 5 come from? It would be
>> nice to not have this automatically displayed.
>> 60 - 80 | 0
>> 80-100 | 5
>>
>
> This comes from my scientific background which says that a legend should
> include information about the frequencies of observations in each class.
> This is what these numbers show. But I agree that this should probably be
> optional.
>
>
>> 2. there could be a flag on d.graph, which allows the output to have a "<
>> minbreak" and "> maxbreak" option, so that for cases like the one we are
>> discussing, the legend does not keep changing based on different data
>> ranges.
>>
>
> d.graph is "just" a drawing module. Any such flags will have to go into
> d.thematic.area, or a specific d.thematic.legend module, but yes, sounds
> good.
>
>
>> 3. size and position
>> Here, I wanted to get a legend file separately, and save a legend png. To
>> do this I had to play with the size and other parameters extensively to make
>> the symbols and associated text match up. It would be great to be able to do
>> the following with some flags, for the case where the legend alone is
>> displayed:
>> (i) set the overall size of the display within which the legend will be
>> displayed
>> (ii) set the position of the legend within the display with options like
>> lowerleft, upperright, center, etc
>>
>
> positioning in d.graph is in percentage, so the size of the display should
> not make a difference for the relative localisation.
>
>  (iii) set the size of the legend as a fraction/percentage of the display.
>>
>
> Size of text is in percentage, but size of symbols aren't. But I guess you
> mean the legend as a whole. There should probably be some way to calculate
> the size of the different elements given a general value from the user.
> Again, this would have to be a parameter for d.thematic.*.
>
>  (iv) make the background transparent (or not)
>>
>
> At this stage the background is transparent, but I could add a flag to
> allow non-transparent (you can do it yourself by just drawing a white
> rectangle underneath).
>
>  such that the above settings 'automatically' set up the symbol and
>> corresponding text all properly lined up..
>>
>
> d.graph does not have any "alignment" feature, you have to work with the
> percentage positioning, but one problem (I think) is that different fonts
> have different sizes, so a same size but different font will lead to
> different alignments.
>
>
>> I am aware that if I was just better at this I could do it quickly
>> enough..but the above functionality would make it easier for
>> less-than-expert people like myself, who try to use open-source as much as
>> possible despite the handicap of having been groomed on Windows...
>>
>
> Cartography is currently one of the weak points of GRASS, although you
> can't beat it for automatic cartography as you are doing (well, gmt can do
> that, but don't know about thematic cartography in gmt).
>
> Thank you for the extensive feedback, though. I get the feeling that there
> should be some d.thematic.legend module which uses the output of the -l flag
> of d.thematic.area to then create a nice-looking legend.
>
> You might also want to have a look at ps.map which allows some more
> sophisticated cartography and offers an automatic legend.
>
> Moritz
>



-- 
Vishal K. Mehta, PhD
Scientist
Stockholm Environment Institute - US
133 D St Suite F
Davis CA 95616
www.sei-us.org
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