fill map with gradient: package?

Hi,
I'd like to fill an existing svg (or png) map with gradient colors.
In detail: The file
http://commons.wikimedia.org/wiki/File:Karte_%C3%96sterreich_Bundesl%C3%A4nder.svg
should be filled with the population density data from this table:
http://de.wikipedia.org/wiki/%C3%96sterreich#Verwaltungsgliederung
choosing the right color saturation (or whatever). The final result
should be something like this map:
http://commons.wikimedia.org/wiki/Image:Bevoelkerungsdichte_-_Oesterreich.svg
Is there a package or so for these two tasks (filling and color
density ploting)?
Thanks for your help,
Thomas