Pedro Cruz has been working on these visualisations of traffic in Lisbon, as part of his thesis. Four types, with the "hotter" colours representing slower traffic & greater congestion.
They look like mammograms to me.
Here's a time-lapse film of one of the treatments.
OPEN YOUR EYES! Musings on what I see around me. What I like and, invariably what I don't. I like to surround myself with beautiful people, and covet beautiful things. I am the emperors new clothes. A modern magpie.