Click here to see the SAS code.
Click here to see the example.

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See my blog for more information!


In this map, there is 1 'dot' per census tract.
The shade of the dot indicates how many people live there
(darker dot = more people).
This is accomplished by overlapping multiple points,
with alpha-transparent color.

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I use the census block map geometry and the %centroid macro to 
get the lat/long centroid of each census block, and then annotate
'points' at those centroids onto our gfk county map (the county borders
you see are from the gfk county map).  

I run the 'points' through a data-step loop to repeat them multiple 
times proportional to the population in that census block -- the 
overlapping alpha-transparent points produce a darker/gradient gray 
(note this does not work prior to SAS 9.4).  
 
I also annotate circles for the cities (I put them behind the map so 
you don't see them, but when you mouse over the city 'clumps' of points, 
you see the city name in mouse-over text).

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