The following image by Mathieu Rajerison has been doing the rounds of French media recently. It shows the streets of Paris, color-coded by their compass direction. It's been featured in an article in Telerama magazine, and even on French TV Channel LCI (skip ahead to 8:20 in the linked video. which also features an interview with Mathieu).
Mathieu used the R language and OpenStreetMap data to construct the image, which colorizes each street according to the compass direction it points. Orthogonal streets are colored the same, so regular grids appear as swathes of uniform color. A planned city like Chicago, would appear as a largely monochrome grid, but Paris exhibits much more variation. (You can see many other cities in this DataPointed.net article.) As this article in the French edition of Slate explains, the very history of Paris itself is encapsulated in the colored segments. You can easily spot Napoleon's planned boulevards as they cut through the older medieval neighborhoods, and agglomerated villages like Montmartre appear as rainbow-hued nuggets.
Mathieu explains the process of creating the chart in a blog post written in English. He uses the maptools package to import the OpenStreetMap shapefile and to extract the orientations of the streets. A simple R function is used to select colors for the streets, and then the entire map is sampled to a grid with the spatstat package, before finally being exported as a TIFF by the raster package. The entire chart is created with just 31 lines of R code, which you can find at the link below.
Data and GIS tips: Streets of Paris Colored by Orientation