New political district maps approved on Monday will color the race to replace Rep. Lynn Woolsey and prompt 7th District Assemblyman Michael Allen to move to advance his political career.

The new maps certified by the state's voter-created citizens commission stretch Woolsey's 6th District — formerly a compact Marin-Sonoma package — to the Oregon border and rename it the 2nd District.

"One big difference is I'll be spending a lot more time in the car," said Norman Solomon, one of four candidates for Woolsey's seat.

Most of the 2nd District's new area was carved out of Rep. Mike Thompson's 1st District, which is renamed the 5th District.

Thompson, D-St. Helena, on Monday said he will run for re-election in the entirely inland 5th District, which includes Santa Rosa and Rohnert Park.

"The district changes and transition will be seamless," Thompson said in a statement. He noted that he has represented some of his new district previously, as a state senator.

In the newly-named 2nd District, with Woolsey retiring next year, Solomon is one of four people vying to take her place in what still will be a largely Democratic district.

Assemblyman Jared Huffman, D-San Rafael, is considered the race's front-runner and his position on issues from foresting to rural funding initiatives will help him further in the new district, said Sonoma State University political scientist Dave McCuan.

But McCuan said the changes will also benefit Solomon, a prominent Marin County activist and author who has positioned himself as the ideological successor to Woolsey, a Petaluma Democrat who will retire in 2012 after completing her 20th year in Congress.

"It counts a lot of progressives, which is helpful for Solomon," McCuan said of the new district.

Solomon sounded that same theme on Monday.

"As a progressive economic populist this is a great shift for me," he said.

Marin County Supervisor Susan Adams and Petaluma Councilwoman Tiffany Renee are also running for the seat. McCuan said Adams' challenges will include marshalling the resources to campaign effectively and raise her profile in the larger district.

In Allen's case, the new maps put his Oakmont residence in the same district as Democratic colleague Wes Chesbro, in the newly named 1st District.

That presents the first-term assemblyman with the choice of running against the veteran Chesbro or moving. On Monday Allen said he will pick up stakes for another district.

"It looks like I'm going to have to move if I want to continue serving," he said.

But Allen's choice remains complicated even then. If he moves west he can fight to represent the newly created District 4, which takes in the Sonoma Valley and Napa, Lake, Solano and Yolo counties.

Or he could move the other way, into Santa Rosa, where he would contend for District 10, which takes in most of Santa Rosa, south Sonoma County and Marin County.

"I do intend to run, I just haven't figured out in which district," he said.

Republican leaders on Monday said they would back a petition for a referendum on the June 2012 ballot to overturn the newly approved state Senate districts, contending they favor Democrats.