The Massachusetts political map has changed over the past four decades, and with it so has the path to the corner office in the State House. As the Commonwealth has morphed from a red and blue checkerboard to solid bands of monochrome, campaigns’ paths to victory are increasingly predetermined.

Instead of fighting town-by-town, Democrats can now focus on running up the score in Boston, the Gateway Cities, and Western Massachusetts. Republicans, meanwhile, must hone in on the central swath between Route 495 and Springfield, attempting to push back the blue tide washing in from the state’s Western border. They also must get back to competing in Boston — not to win, but to keep the Democrats’ margin in the capital from swamping them elsewhere.

Unlike previous maps showing the two parties’ vote share, this set of maps shows each town’s distance from the statewide margin in each gubernatorial election since 1970. Distance from the margin shows relative partisan voting of each town. Thus, even in a blowout election, we get a sense of which towns are relatively more Democrat or Republican than the state as a whole.

Here’s the map of Deval Patrick’s 2010 win over Charlie Baker.

And here is a very different looking map, from Democrat Edward King’s victory in 1978.

Some quick takeaways:

  1. Boston is Republicans’ biggest problem. Hiding in plain site on the map is the treasure trove of Democrat votes in Boston. While other towns have gone deeper blue in percentage terms, a somewhat smaller percentage shift in Boston nonetheless translates into a big gain in raw vote. Charlie Baker doesn’t have to win Boston, but he has to compete; otherwise, the lead his opponent builds there could be difficult to overcome.
  2. Western Mass is now a sea of blue. Up until 1998, the Western third of the state was a battleground, with towns flipping from red to blue from election to election. Since 2002, this is no longer the case. Towns on the western border of the state went for Deval Patrick by an average of 55 points in 2010 and for Ed Markey in his Senate race last year by 49. To regain statewide competitiveness, Republicans will need to stem the tide of blue washing in from the state’s western border. When Scott Brown won in 2010, there was less deep blue there, and it stopped shorter. Later that year, Deval Patrick ran up the score in the west and went on to victory.
  3. Central Mass is much deeper red. It’s no accident that Charlie Baker’s running mate Karen Polito is from Worcester County, the center of the target for Republicans trying to turn out the base. Big margins in this area are key to Republican success. This area has voted more and more Republican in recent decades, and is now their key to victory. Scott Brown won Worcester County by 61,000, twice as a large a margin as he ran up anywhere else.
  4. Border wars. If Democrats have made gains along the state’s Western border with New York, the GOP is building a stronghold of its own along the northern line with New Hampshire. The gateway cities of Lowell and Lawrence are spots of blue among the deep red spreading from the north-central part of the state into the Merrimack Valley.
  5. Split south of Boston. Democrats win the outer Cape and the Islands and the South Coast cities of New Bedford and Fall River, but territory between there and Boston is now deep red.

Click here for a PDF containing maps for everyone governor’s race since 1970. And click here to access the full dataset behind these maps, and to generate your own interactive versions.