RALEIGH With colorful maps and charts as their backdrops, lawyers began making arguments on Monday about a legal challenge to North Carolina legislative and congressional districts drawn two years ago by the Republican-led General Assembly.

Attorneys for Democratic voters and a coalition of civil rights and election organizations were the first to rise before a three-judge panel. They contend the new maps are unconstitutional.

The ultimate shape of the maps could determine which party holds power in North Carolina for the next decade.

On the challengers’ side, attorneys argue that mapmakers working for the Republican Party drew the lines to concentrate black voters in districts that reduce their overall political power.

Attorneys for the GOP legislative leaders and the state, who are set to begin their arguments on Tuesday, contend the lawsuit should be dismissed, arguing that the redistricting passed muster with Washington and is really no different from what Democrats did a decade ago.

Under the Voting Rights Act, the U.S. Department of Justice gets to weigh in on the mapping to protect against racial discrimination. In November 2011, Justice Department officials said they would not oppose the maps based on grounds of discrimination.

Attorneys Anita Earls and Allison Riggs of the Southern Coalition for Social Justice in Durham, Edwin Speas of Poyner Spruill in Raleigh and Adam Stein of Ferguson, Stein, Chambers, Gresham and Sumter in Chapel Hill spent the morning and afternoon in an airy courtroom at Campbell University law school describing the problematic districts to Paul Ridgeway, Joseph Crosswhite and Alma Hinton, the three Superior Court judges presiding over the hearing.

The attorneys contend the 2011 election district maps are illegal, in part, because they split voting precincts and fail to keep whole counties within districts.

The new lines divide neighborhoods and apartment complexes and, in at least one case, cross through a house, leaving voters and candidates confused about who’s in what precinct, argued attorneys for the map challengers.

By shaping districts that way, the mapmakers weaken the power of the black vote in other districts. Some of the districts being challenged are in Wake and Durham counties.

N.C. in the spotlight

Redistricting occurs every 10 years based on the national census. In 2010, Republicans took control of both chambers of the General Assembly for the first time in more than a century and led the redrawing of the lines.

That process has gotten much attention nationally.

Earlier this month, The New York Times published an opinion piece by Sam Wang, the founder of the Princeton Election Consortium and an associate professor of molecular biology and neuroscience at Princeton University. In his piece, titled “The Great Gerrymander of 2012,” Wang pointed out that, nationally, Democrats received 1.4 million more votes than Republicans for U.S. House of Representative seats in 2012, but the GOP won control of the House by a 234 to 201 margin.

Wang pointed out that North Carolina was one of five states where the party that won more than half the votes did not get at least half the seats. In North Carolina, where the two-party U.S. House vote was 51 percent Democratic and 49 percent Republican, nine Republicans and four Democrats were elected.

“If districts were drawn fairly,” Wang surmised, “this lopsided discrepancy would hardly ever occur.”

Thomas Hofeller, a seasoned GOP mapmaker cited by lawyers at Monday’s hearing as one of the chief architects of the 2011 N.C. maps, was featured in “The League of Dangerous Mapmakers,” an article published in October 2012 by The Atlantic.

“Every 10 years, after U.S. census workers have fanned out across the nation, a snowy-haired gentleman by the name of Tom Hofeller takes up anew his quest to destroy Democrats,” Robert Draper reports in the piece.

How big a role did race play?

Attorneys for Margaret Dickson, one of the Democratic plaintiffs, and the North Carolina State Conference of Branches of the NAACP argue that race played a large role in the shaping of the maps that Hofeller designed for North Carolina.

In 1965, the Voting Rights Act was adopted to give federal officials an oversight tool to foil persistent efforts in some states to keep blacks from voting.

In addition to needing a blessing from Washington, D.C., to make elections changes, the act allows for poll watchers and other safeguards against electoral racism.

But on Wednesday, the U.S. Supreme Court will hear arguments in a case from Shelby County, Ala., which deals with a clause in the landmark legislation that allows local, county and state governments an escape hatch from oversight provisions of the decades-old act.

Though rarely granted, governments are supposed to be able to get out from under needing federal monitoring for redrawing electoral districts or move polling places if they can prove past success in protecting minority voters.

Opponents of the “preclearance section” of the Voting Rights Act say they no longer should be forced to live under the federal oversight. They cite the re-election of President Barack Obama as demonstration of enormous racial progress over the past 40 years.

In 2006, President George W. Bush signed a 25-year extension of the clause. It currently applies to Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. It also covers certain counties in five states, including North Carolina.

When, when not to use race

As he listened to the arguments on Monday, Ridgeway asked the attorneys for those challenging the districts to help him reconcile the need for mapmakers to consider race when drawing districts for the counties that still fall under the preclearance clause, but not allowing it to play a role in the shaping of other districts.

“When is it wrong to use race as a factor and when is it OK?” Ridgeway asked.

Modern redistricting, Earls responded, allows the lawmakers cognizance of racial demographics, but does not permit them to use it as a predominant factor.