(Harrisburg) -- The five-member panel tasked with redrawing legislative districts is slated to meet later today to vote on a rough draft of the new map. What was unclear two months ago is almost certain now. Redrawing state House and Senate districts based on new population data will likely require one or two Senate districts to be moved completely -- says Erik Arneson, Senate GOP spokesman. "We don’t see a way to draw a map for the Senate that does not move one or two districts from the western half of the state to the eastern half of the state, due to the population changes that have happened over the last 10 to 20 years," he says. Exactly which districts may be picked up in the west and plopped down in the east will become clear if the state’s Legislative Reapportionment Commission approves a preliminary district plan today. It’s possible the panel's nonpartisan chairman could vote against every plan offered by the legislative caucus leaders on the commission. But if a proposal is approved, it sets a 30-day clock ticking -– that’s how long the public will be able to comment on the plan before it is finalized with another commission vote.