Not every Twitter user geotags their musings, but there are enough who do to generate some very insightful data. On its blog today, Twitter shared images from Data Visualization Scientist Nicolas Belmonte, who created topographic maps visualizing the density of geotagged tweets. The result is striking, as tweets clearly correlate with roads, geographic features and even lines of public transit. In addition to the blog's stills, you can futz around with interactive maps of New York, San Francisco and... Istanbul. When you realize the implications of all those tweets from the Bay Bridge, it's frightening enough to consider taking BART across the Bay instead.