## A Map of County Population Change Relative to US Population Change

In the above map, I've tried to represent the population change of counties relative to the population change of the country at large. The challenge was to find an algorithm that would consistently represent this relationship across any arbitrary length of time. I'm not sure I succeeded but I thought the results were interesting. The map lets you pick a start and stop census year. You can then calculate and represent a quotient for each county. This is: percent change in county population divided by percent change in US population. You can also calculate the number of standard deviations a counties' population change was from the mean population change. Since some counties, especially in the early 1800s, increased in population thousands of percent, this didn't always work very well. To get the distribution closer to normal, I adjusted very high values down. Both standard deviations and quotients can be animated in ten year steps from 1820 to 2010. This map was made with Mapbox.js and uses slightly improved census data from the NHGIS.

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