The Alaska Supreme Court ruled Friday that a new map of state Senate districts for Anchorage “constituted an unconstitutional political gerrymander violating equal protection under the Alaska Constitution” and must be redrawn before its use in this year’s statewide election.

In a combined summary decision, the court said it is upholding a lower court ruling that instructed the state’s five-person redistricting board to redraw the Senate map or explain why it is impossible to do so.

As part of the decision that combined several lawsuits against the redistricting maps, the justices ru...