The city of Madison is in the beginning stages of redistricting, which is required by state law and must be finished by Dec. 31.

City Council members are being briefed about possible additions to and subtractions from their districts, which are supposed to each contain about the same number of people, mayoral aide Bob Cooke said.

Redistricting must be done after every 10-year census.

Cooke said he hired FPBH Inc. in North Vernon to draw proposed maps. Cooke said the maps are likely to be discussed by a council subcommittee, then presented as an ordinance to the City Council. There will be a public hearing as part of the ordinance process.

Madison's redistricting has drawn the interest of the Massachusetts-based Prison Policy Initiative because the population of the Madison Correctional Facility on the hilltop, a state women's prison, is included in the city's total population even though the prisoners cannot vote.

The result, initiative legal director Aleks Kajstura said Friday, is that one council district gets more clout than the other districts.

"Called prison-based gerrymandering, the practice finds its clearest example in Anamosa, Iowa, where a large prison was almost an entire city council district," the district said on one of its websites, www.prisonersofthecensus.org.

"Council districts are supposed to contain the same number of people, but basing districts on non-voting non-resident prison populations gives a handful of residents the same political power as thousands of residents elsewhere in the city," the website said.

Terre Haute this year decided to exclude prisoners from its calculations.

The women's prison is in City Council member Pete Backus' District 3.