Binning (hexbins)

Use binning to create better scatter plot maps.  
- What is it?
- Who's doing it?
- Why/when should I do it?
- How do I do it?

https://www.mapbox.com/blog/binning-alternative-point-maps/
http://indiemaps.com/blog/2011/10/hexbins/

Possibly related to #17 
