Any globetrotting tourist will tell you that all cities are unique. The challenge is to figure out what they have in common. Fortunately, there's at least one thing that is nakedly apparent for every single city: the contours of its streets as seen from outer space. A team of researchers has now taken those street maps and analyzed them as mathematical networks. It turns out that all cities can be boiled down to just four different types based on the "fingerprint" of their street networks, the team reports online today in the Journal of the Royal Society Interface: a grid of medium-sized blocks that are mostly square or regular rectangles, a dominant fraction of small blocks with a diverse array of shapes, mostly medium-sized blocks with diverse shapes, or a mosaic of patches of mostly small squares or rectangles. For example, those who say that American and European cities tend to be "laid out differently" now have mathematical evidence. Boston's famously confusing street map—which produces small and diversely shaped city blocks—is more like a European city’s than that of the typical gridlike U.S. city. And some of the largest cities are revealed to be a hodgepodge of different parts. The five boroughs of New York City (above) are closer matches to different cities around the world than they are to each other. Manhattan has the gridlike street layout of Brazilian cities like Campo Grande and Curitiba, while the Bronx’s streets look like those of Porto, Portugal. Brooklyn is strikingly similar to Detroit, Michigan, at least in layout. And Staten Island? It’s like walking the streets of As-Suwayda, Syria.