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The U.S. Supreme Court on Friday refused to intervene in a lengthy dispute over redrawing Chicago’s ward map.

The action leaves intact an April ruling by a federal appeals court in Chicago that rejected a remap that created 19 wards with predominantly black populations.

Meanwhile, a federal judge in Chicago, given 90 days by the appeals court to make changes to the map, decided Friday to limit her review to two almost identical proposals that would make the 18th Ward the city’s 20th black-majority ward.

U.S. District Judge Elaine Bucklo gave attorneys for some of the African-American plaintiffs until Wednesday to submit in writing reasons she should alter the 18th Ward boundaries so its population is 74 percent black.

Under the map rejected by the 7th U.S. Circuit Court of Appeals, the Southwest Side 18th Ward was considered a white ward even though its black population slightly exceeded 50 percent. The defendants will have another week to show why the change would be unfair.

Bucklo said she would decide then whether she needs to hold hearings and take evidence.

In its decision in April, the appeals court suggested that creating one more black ward at the expense of one of the current white wards “might well achieve an almost exact proportional equality of voting power between black and white.”

The city map had established 24 white wards and seven Latino wards in addition to the 19 black wards.

In ordering the case back to the federal court, the appeals judges imposed a 90-day deadline to make changes to the ward map so it’s in place in time for aldermanic elections next year.

After court, Jerold Solovy, an attorney for a group of aldermen who support the current map, said the whole exercise is unnecessary because updated demographic data show that the 18th is now overwhelmingly black.

But Judson Miner, an attorney for some African-American plaintiffs, said the map must be based on 1990 census figures. If updated demographics were used, Miner said, there should be two additional black wards, not just one.

Chief Judge Richard Posner of Chicago’s federal appeals court said in an April ruling that as “a rule of thumb,” blacks must be at least 65 percent of the total population of a district to elect a black official. The reason, he explained, was that blacks have a younger population and fewer registered voters.