Another federal census, another legislative redistricting process, another opportunity for politicians to try to manipulate that process for their and their party’s gain.

Across the nation, federal, state and local legislative district lines are about to be redrawn to reflect shifts in population revealed by the 2010 census. That process looks to be particularly painful in Massachusetts, which is due to lose one of its current 10 Congressional seats—a seat, many observers speculate, that will come from the western part of the state.

Redistricting is an age-old process mandated by the U.S. Constitution—and an age-old opening for political gerrymandering. Indeed, according to the makers of a new documentary on the subject, the very term “gerrymander” was coined 199 years ago, right here in Massachusetts, when Jeffersonian Republicans tinkered with district lines to improve their odds in an upcoming election. One contorted, elongated district in the eastern part of the state bore such a resemblance to a salamander in the eyes of a newspaper editor that he dubbed it a “gerrymander,” after then-Gov. Elbridge Gerry, who’d signed the redistricting legislation.

Gerrymandering is also the name of the documentary, written and directed by Jeff Reichert and produced by Green Film Company. It will be shown in Northampton at Smith College on Thursday evening.

The film, in the words of its makers, “exposes the most effective form of manipulating elections short of outright fraud.” It includes a look at four common forms of gerrymandering, named, rather colorfully, “packing” (filling a district with voters of a common type to minimize the number of total districts they can influence); “cracking” (a reverse of packing, in which those voters are spread over so many districts that their vote is diluted and therefore unlikely to have much effect); “hijacking” (when a district is drawn to separate an incumbent from his or her current constituents to diminish his or her chances of reelection); and “kidnapping” (when a new district is created to pit two incumbents against one another in the next election).

The film also includes a segment of prison-based gerrymandering—an often-overlooked practice that’s been well documented in the work of Easthampton’s Prison Policy Initiative—in which prisoners who lack the right to vote are nonetheless counted in redistricting figures. That, PPI’s research shows, creates an imbalance that’s particularly profound in places like New York, where the rural upstate, home to many state prisons, gains more legislative seats than its nonprison population would dictate thanks to the presence of people who have no say in those elections. Meanwhile the areas of the state where the prisoners do come from suffer, since the prisoners are not counted in the census in their hometowns. (See “The Prison Town Advantage,” Oct. 8, 2009, www.valleyadvocate.com.)

After the local screening, PPI Executive Director Peter Wagner will lead a discussion about the issue of gerrymandering, including efforts to reform prison-based gerrymandering.

Gerrymandering will be shown on Thursday, April 14, at 7 p.m. in Smith College’s Seelye Hall, room 106. The screening is sponsored by Smith Students for Social Justice and Institutional Change.