The map's creators, Viegas and Wattenberg, gave a talk on how they made the visualization at the Eyeo Festival 2012 -- https://vimeo.com/48625144#t=16m55s https

The map's creators, Viegas and Wattenberg, gave a talk on how they made the visualization at the Eyeo Festival 2012 -- https://vimeo.com/48625144#t=16m55s https://vimeo.com/48625144#t=16m55s . They show the experiments that took them from static vector fields to the fading brushstrokes analogy: Static vector field: https://vimeo.com/48625144#t=20m34s https://vimeo.com/48625144#t=20m34s | Particles: https://vimeo.com/48625144#t=21m16s https://vimeo.com/48625144#t=21m16s | Particles with geographic outlines: https://vimeo.com/48625144#t=21m47s https://vimeo.com/48625144#t=21m47s | Warping blocks: https://vimeo.com/48625144#t=22m21s https://vimeo.com/48625144#t=22m21s | Static brush strokes: https://vimeo.com/48625144#t=23m16s https://vimeo.com/48625144#t=23m16s | Fading brushstrokes: https://vimeo.com/48625144#t=24m57s https://vimeo.com/48625144#t=24m57s