Excellent work [1] using OSM as source for an analysis of street names in Germany. Even if you do not speak any German, the maps speak for themselves. Bonus: Source data available.
[1] http://www.zeit.de/feature/strassenverzeichnis-strassennamen-herkunft-de...
I heard about this question several years ago. I was surprised to know the answer: we just need four colors to be able to color any map without two colors touching each other. However, I couldn't clearly understand why. It is not surprise, this questions haunted geographers and mathematicians for 125 years, until it was proofed to be right in the 1970's... However, the proof of 'the four color map theorem', as it is called among mathematicians, it remains as a not "beautiful" proof.
