Gov. Deval Patrick (D) signed into law a new map that drops the number of congressional districts in Massachusetts from 10 to nine, his office confirmed.

The map Patrick signed creates the state's first majority-minority district and shores up a number of incumbents among the state's all-Democratic congressional delegation.

Massachusetts lost one seat in the House due to slower-than-average population growth in the once-per-decade redistricting process. But a serendipitous retirement by Rep. John Olver (D-Mass.) spared Democrats the ugly process of pitting two incumbents against each other in a primary.

Although Massachusetts Reps. Bill Keating (D) and Stephen Lynch (D) were both drawn into the same district, Keating will be able to run in another district, where he owns a vacation home.

- This post was updated at 6:01 p.m.