[postgis-users] Thematic mapping with PostGIS

Dane Springmeyer blake at hailmail.net
Mon Feb 11 08:43:29 PST 2008

Doug, I would also recommend uDig as a good route.

Styling, using SLD in uDig great (Layers>Change Style>Theme), however  
currently I'm only aware that Equal Interval and Quantile themes are  
exposed in the application. A natural breaks algorithm would need to  
be added, and how to go about that might be a good question for the  
udig developers: udig-devel at lists.refractions.net. I'm pretty sure  
that uDIG depends upon geotools/colorbrewer code to do styling  
(www.colorbrewer.org/), so a lot of great styling options area likely  
possible in future releases of uDig.

Another route I've pursued for styling polygon data is to use python  
or PHP to pull data directly out of postgres and into custom styled  
KML for viewing in Google Earth. Members of the list help get me  
started doing this. The basics are to use the AsKml(geometry)  
function and then wrap the resulting kml geometry in the proper KML  
header, styles, and footer. I find this easiest to do with python.  
I've started using an XML templating system to make this even easier  
when needing to style data in a variety of ways.

The nice thing about a scripted approach outside of postgres is that  
once you've tweaked your script to style you data exactly how you  
want you can easily set it up as a cgi script on your local or remote  
server. A KML network link from within google earth can then hit your  
script via a browser to regenerate your KML and sent it back to  
google earth automatically. You can embed your SQL routine inside the  
script and just go back and forth between the editing the SQL inside  
the script and your GE display or just have the script pull from a  
database view that you keep writing over from some other SQL  

Overall, if you just want to see your data quickly this is not the  
right route. But if you are interested in tapping the visualization  
possibilities of google earth it is well worth it. I'd be happy to  
send code snippets if you are interested.


On Feb 9, 2008, at 4:26 PM, Dan Putler wrote:

> Hi Jim,
> QGIS (which is what I assume you mean by "Quantum") allows you to  
> create
> thematic maps using PostGIS layers. Go to the properties of a layer  
> and
> muck with the legend type. Alternatively, you can load PostGIS layers
> into uDig (http://udig.refractions.net), and alter the style of a  
> layer.
> Dan
> On Sat, 2008-02-09 at 19:08 -0500, Doug Foster wrote:
>> I am new to PostGIS, and want a good Windows desktop mapping tool to
>> view and thematically map boundary data from my PostGIS database.  I
>> have Quantum, which is a nice viewer, but it doesn’t seem to do
>> thematic mapping.  I am a heavy MapInfo and Maptitude user, but they
>> don’t read PostGIS spatial boundaries.  I wish they would.
>> Is there a free/inexpensive tool to view and do some nice thematics?
>> I would also like to have the “natural break” routine, which I use by
>> default since it’s the beast way to break up the categories.
>> I have been doing all my database work in SQL Server and then linking
>> from MapInfo and linking with equivalent boundary files (census block
>> groups and zip codes for all USA).  That’s for the birds when I’m
>> running routines in SQL Server and want to view the results
>> graphically on an interactive basis.  It’s very clumsy.  So
>> PostgeSQL/PostGIS is a much better solution but I haven’t found a  
>> good
>> way to view the results spatially.
>> Thanks…..
>> Doug
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> -- 
> Dan Putler
> Sauder School of Business
> University of British Columbia
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