How about starting with a data density app?
If you search on my name and "data density" you'll find some routines on the web, but that would be cheating. The way the system works is to take reciprocal of squared distance plus a fudge factor to prevent 1/d when the sample pixel point is very close to a data point. So you get the density of a 2D scatterplot.
You then need a nice visual representation of a linear scale, using colours to represent value changes. I'll give you those, I have several colour palettes at
http://www.malcolmmclean.site11.com/www/datadensity/colourschemes.c
http://www.malcolmmclean.site11.com/www/datadensity/colourschemes.h