Louisiana’s newly designed 2nd Congressional District doesn’t look like it makes much sense — one end of it starts in a tip just north of Baton Rouge, and from there it juts and jags its way more than 70 miles south and east past New Orleans, seemingly picking up random communities along the way.

Most of the people who live in those communities are African Americans, joined together partly by design and partly by law. By looping African Americans into one district, lawmakers increased the number of Republicans in surrounding districts, virtually ensuring that the GOP will hold a major advantage in five of the state’s six congressional districts for the next decade.

As lawmakers across the nation begin the once-a-decade process of redrawing their congressional boundaries, a significant migration of blacks from cities to suburbs is having a widespread political impact.

According to newly released census numbers, eight of the nation’s top majority-black districts lost an average of more than 10 percent of their African American populations. That will provide an opportunity for Republican lawmakers, who control an increasing number of statehouses following last fall’s elections, to reshape districts in suburban swing areas of Michigan, Pennsylvania, Ohio, Georgia and elsewhere.

Dozens of seats could become easier for Republicans to hold on to, with a half-dozen or so becoming prime pickup opportunities for the party, according to political strategists.

“The practical effect is great for the GOP,” said Dave Wasserman of the Cook Political Report. “In state after state, it’s allowing Republicans to pack more heavily Democratic close-in suburbs into urban black districts to make surrounding districts more Republican.”

The migration of blacks to the suburbs is also having an impact in the Washington area, where the African American population in the District dropped 11 percent over the last decade, while suburban Rep. Steny H. Hoyer (D-Md.) gained more black voters than anyone outside of the fast-growing Atlanta area.

Fellow Maryland Democrats Donna F. Edwards and Chris Van Hollen also gained large numbers of black voters. Unlike some other places, though, those lawmakers are not likely to be greatly affected, since Democrats control the redistricting process in Maryland.

The 1982 amendment of the Voting Rights Act led to the creation of many legislative districts, particularly in the South, in which minorities became the majority populations. The idea was to give minority voters a chance to elect candidates of their choice. Over time, these districts encountered legal challenges and setbacks, including at the Supreme Court, over questions of racial gerrymandering.

Initially, these districts were a boon to Democrats, creating opportunities in places where the party struggled to win. But over the last few rounds of redistricting, Republicans have made a habit of “packing” as many reliably Democratic black voters into as few districts as possible, virtually guaranteeing black representation for those districts while also making nearby ones more winnable for the GOP.

So even as the African American population has been shrinking in many longtime black districts, the number of majority-black districts has actually increased over the last decade — and could very well continue to do so, with Republicans leading the redistricting process this year.

Reshaping the suburbs

The relocation of large numbers of African American voters will likely lead to substantially different districts outside several major cities.

In the Detroit area, for instance, Democratic Reps. John Conyers Jr. and Hansen Clarke lost nearly one-quarter of the 800,000 black voters in their districts since 2000, with many of them migrating to nearby districts. The expansion of Clarke’s and Conyers’s districts could help Michigan Republicans eliminate a Democratic district in the area.

The same goes in Ohio, where Rep. Marcia L. Fudge’s (D) loss of 29,000 black voters means that her district will have to grow and Republicans can more easily collapse some nearby Democratic districts.

There is also an opportunity for the GOP to create some new black-majority districts. If Republicans make the district of Rep. Sanford D. Bishop Jr. (D-Ga.) majority black, it could help keep freshman Rep. Austin Scott (R-Ga.) safe by taking Democrats out of his neighboring district. And Republicans could push Rep. Robert A. Brady (D-Pa.), a white Democrat whose district is primarily in Philadelphia, into a majority black seat, a move that might help them shore up all the suburban seats they hold nearby.

In Louisiana, the current New Orleans-based 2nd District lost nearly 120,000 black residents over the past decade, largely due to Hurricane Katrina. In order to keep the black population as high as it was before, the district had to be expanded significantly, reaching to the state capital of Baton Rouge.

As a result, the Baton Rouge-based 6th District, which Democrats held briefly last decade, dropped from 34 percent black to 24 percent black.

“It keeps those districts a lot safer for those guys,” said Louisiana political analyst John Maginnis.

Hilary Shelton, the Washington bureau director for the NAACP, said his organization is prepared to fight the over-packing of majority-black districts and hopes that Republicans won’t overplay their hand.

“On one hand, we like to see cohesiveness of those who share common values,” Shelton said. “But it is important that we don’t end up with the kind of packing in districts that” diminishes the influence of black voters.