Answer to Map #6

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Back to this week’s map and hints.

Answer: This is a proportional symbol map in which each circle represents a city that has a functioning subway or metro system, and in which the size of the circles are proportional to the number of stations that system has.

For this map, some users submitted solutions that were close to correct, but not quite precise—either they guessed that the dots corresponded to the total length of track of the subway system or to the total number of passengers using the system. Neither of these answers is quite correct, but we awarded half credit (and half the number of points!) to those who submitted them. The key to figuring out the precise answer was the recognize that London, Moscow, and Seoul were not among the cities with the largest dots. The London Underground has the third longest total track length in the world (behind only Beijing and Shanghai), but it has fewer stations than Madrid and New York. The Madrid Metro is a remarkable 25th in the world in terms of total number of riders, yet it is in the top five (ahead of London) in terms of number of stops. If you want to investigate these rankings further, check out Wikipedia’s helpful list of the world’s metro systems. Of course, there are multiple definitions of what constitutes having a “metro system,” and we have used a definition that rules out light rail systems. It is what it is. Please don’t write in to complain that we have forgotten the Docklands Light Railway.

On this map, the largest red dots indicate cities with more than 300 subway stations. The orange dots correspond to cities with 200-299 stations, the yellow dots to cities with 100-199 stations, the green dots to 50-99 stations, the light blue dots to cities with 30-49 stations, the navy blue dots to cities with 15-29 stations, and the purple dots to cities whose subway systems have fewer than 15 stations.

Collectively, this week’s hints paint an interesting picture of the stages of subway construction in the world. The London Underground, whose Metropolitan Line opened in 1863, was the first underground railway in the world. It then took more than three decades before other cities began to build subway systems of their own. Around the turn of the century, an assortment of cities in Western and Central Europe and in the eastern half of the United States began to open new systems—hence Thursday’s hint about what the map would have looked like in 1901. After World War II, the Soviet Union placed a particular emphasis on building large-scale infrastructure projects in the cities under communist rule’hence Tuesday’s hint pointing out all the dots in provincial cities of the former Soviet Union. Today, the cities that are most active in building transportation networks that can accommodate their large populations are in Asia—hence Friday’s hint about what will be added to this map in 2017.

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