SPRINGFIELD — A bipartisan coalition of state lawmakers and advocacy groups announced an effort in both chambers Thursday to overhaul the way Illinois’ legislative districts are drawn. Legislators from Chicago, its suburbs and downstate are backing a state constitutional amendment — twin measures in the Senate and House — shifting district mapmaking power from politicians to a 17-person commission whose members would be representative of state demographics. In three news events across Illinois on Thursday, backers of the plan said the measure they call the “Fair Maps Amendment,” more than any of the other redistricting reform proposals, is “comprehensive,” “equitable, transparent, representative, and provides meaningful participation.” The amendment is backed by the same group that attempted to reform the redistricting process in the past three elections, CHANGE Illinois — the Coalition for Honest and New Government Ethics. “As a sprawling federal corruption investigation continues, we should start to end corruption by ending gerrymandering where it begins when maps are drawn,” Madeleine Doubek, the group’s executive director, said.