From the outside, Massachusetts appears as blue as a state can be. But as Steve Koczela’s article in today’s issue of CommonWealth explains, the Bay State, like the rest of the country, is undergoing its own political polarization. Blue towns are getting bluer, red towns are getting redder, and fewer towns are anywhere in the middle. While the overall state averages don’t show it, the margins in recent state elections are the result of two political groups marching steadily in opposite directions.

What’s more, entire regions are taking on a uniform, deep colors, potentially transforming the electoral calculus for statewide office-seekers. In the 1970s through the mid-1990s, a close election would leave an electoral map that looked like a checkerboard. Republican towns and Democrat towns intermingled, with no real regional strength (other than the city of Boston itself) for either party. Recently however, the state has broken up into regions, with a deep blue area in the western part of the state, another in Boston, with essentially everything in between red.

Due to a technical glitch, the maps with the print issue of the magazine were incorrect and don’t show the true extent of this regional effect. (They are correct in the online story linked above.) Below are the two corrected maps, for the Senate races in 1982 and 2013. The colors are based on two-party vote share: the margin between the two major party candidates when counting only Democrat and Republican votes.

1982 Senate:

2013 Senate (Special Election):

You can also view this PDF to see all the maps for each Senate and Governor’s race going back to 1970. You can see clearly the evolution of the map from the more scattered colors of the 1970s and 1980s to what are now distinct regions.

As the tech-saavy among you may have noticed, we have produced these maps using Google’s Fusion Table tool. We plan on doing more with this dataset in the future, so stay tuned.