Hi,

I am using maptools to plot air quality data on a map. Each measurement point is mapped to a postal code area. This yields pictures with discrete borders, like so:
http://dl.dropbox.com/u/27415200/baincome.png
The problem is that the size of a postal code area doesn't mean much in this context. Moreover, only a small minority of all the postal code areas has a measurement sation. Are there any ways/tools to "interpolate" the various (strategically chosen) measurement stations? I am looking for sensible ways to create plots like this:

http://matplotlib.github.com/basemap/_images/etopo5.png

> sessionInfo()
R version 2.11.1 (2010-05-31) 
i686-pc-linux-gnu 
...

 
Thank you in advance!


Cheers!!
Albert-Jan


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All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?
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