To try to solve this geographical problem, Garrett Nelson of Dartmouth College and Alasdair Rae of the University of Sheffield used census data on more than four million commuter paths and applied two different analyses, one based on a visual interpretation and the other rooted in an algorithm developed at MIT. Their results and maps appear today in the open-access journal PLOS ONE....But where should planners draw the edges of a megaregion encompassing this activity? Which connections are statistically significant? Which are important for regional transit planning? Should they focus on the cities surrounding the bay, or is Sacramento just as important to the Bay Area economy?I would guess selecting the number 50 explains the region I live in, which covers Cincinnati, Dayton, Lima, Columbus and areas down to southern West Virginia. Regardless, that is a pretty cool map. If one were to make a map of my drives, it would be dominated by a small triangle between my house, my job and the farm where my cows are, with a few small detours for feed, food and beer. It would dominate a small portion of my county. I honestly can't imagine a daily commute to Columbus. I thought 20 miles to the next county's seat was pretty long.
For answers to these questions, Nelson and Rae turned to an algorithm-based tool designed by MIT’s Senseable City Lab to mathematically recognize communities. The algorithm only considers the strength of connections between nodes (more than 70,000 census tracts in this case), ignoring physical locations. This made for a nice test of Waldo Tobler’s “first law of geography”: that things that are near each other are more related than those that are farther apart....
One of the decisions the researchers made was to limit the algorithm to 50 megaregions, which can be seen in the map above, where every node is colored according to the region it belongs to. This made the map more plausible visually. While 50 may sound like an arbitrary number, it makes sense mathematically because a very high percentage of commutes lie entirely within a megaregion relative to paths that cross boundaries between regions.
Tuesday, December 6, 2016