Open source map design studio for creating custom web tile maps that use MapBox's data.
For novices to GIS, TileMill is great for 'faking' heat maps using the CSS styling tools. Simply increase the size of each GIS point and play around with the opacity (0.2-0.4 works well) to acheive a blending effect. A crude of example of my own (which I mocked up having played with TileMill for only a few hours) can be found here: https://www.dropbox.com/s/gl1e8fcj2l8lelj/PO%20Trades.png
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