Pennsylvania gained population in the census – but the commonwealth will still lose one congressional seat in 2013. Pennsylvania has been steadily losing seats in every census since 1920, when it had 36 representatives. State Senate Republican spokesman Erik Arneson says, viewed in that light, this year’s news was good. “We did better than we have done since 1940,” he said. “But you have to go back to 1920 to find a year where we didn’t lose at least one; 1910 we had 36, 1920 we had 36. Every 10 years since then we have lost at least one, and most often two or three members of the U.S. House.” The state Senate and House will need to draw up the new districts next year. They’ll do so through the regular legislative process, rather than General Assembly redistricting, which is accomplished through a special committee. Arneson said the work likely won’t get started until the summer or fall. “Although we have statewide numbers right now, and we know what Pennsylvania’s statewide population is, we don’t have county, municipal or even precinct-level data,” he said Tuesday. “And we need those things to be able to draw congressional districts.” There’s no legal deadline for redistricting, but the process needs to be complete by January 2012, when prospective candidates begin circulating nominating papers.