As we’ve been documenting in our ongoing series, political parties and other powerful players use the once-a-decade redistricting process to advance their own goals — often at the expense of voters.

A recently released trove of email messages from Ohio offers a rare inside glimpse into how it works.

The messages, sent from June to September, show collaboration between the national GOP and state Republicans to redraw Ohio’s maps and thus cement control of both the statehouse and a majority of congressional districts.

In one email, a Republican consultant working on redistricting for the state suggested that the new political maps could save the GOP “millions" of dollars in campaign funds by making districts safer for Republican candidates.

The maps, approved by the Republican-run state legislature in September, favor Republicans in 12 of Ohio’s 16 new congressional districts. And they strengthen the majority of likely Republican supporters in at least 17 state house districts, according to the mapping consultants' own calculations.

The congressional maps also split voters in Toledo into three separate districts, a move the mayor said would make the city “politically irrelevant,’’ and put two longstanding Democratic members of congress who live 110 miles apart in the same district, a tactic redistricting experts call "hijacking." (See our rundown of various redistricting techniques, such as packing, cracking and hijacking, or watch our redistricting music video.)

A spokesman for Ohio’s House of Representatives said the email messages and accompanying report, released by the Ohio Campaign for Accountable Redistricting, were an attempt to garner “salacious” and “malicious” headlines. Mike Dittoe, director of communications for the Ohio House of Representatives and for Republican Speaker Bill Batchelder, said Ohio’s redistricting was “a fully transparent process that yielded a fair and legal map.”

Redistricting is supposed to benefit voters by equalizing districts as the nation's population shifts. But with few strict requirements for how to shape districts — they must have roughly equal populations and not discriminate against minority voters — political parties often can draw political lines largely to their own benefit.

Much of the time, the toughest balancing act in the map-drawing process is how to please multiple incumbents at once.

In the email messages obtained by the Ohio Campaign for Accountable Redistricting, such partisan concerns were central. In one email, the president of the state senate, Republican Thomas Niehaus, noted that "I am still committed to ending up with a map that Speaker [John] Boehner fully supports," even though the U.S. House speaker and Ohio Republican "has no official role in the redistricting process," as a spokesman said in November.

Among those consulting closely by email regarding the district lines was the executive director of Team Boehner, a group created to help Republican House candidates across the nation, and the redistricting coordinator from the National Republican Congressional Committee. Rather than work in the state house, the state’s redistricting staffers rented a hotel room for three months.

Dittoe, the House spokesman, said the state received redistricting input from many stakeholders, including all 18 of Ohio’s current members of Congress — Ohio loses two seats in the latest redistricting — and Ray Miller, a former Democratic state politician.

The redistricting consultants also pushed through an 11th-hour change to the maps that switched the location of The Timken Company back to the district of U.S. Rep. Jim Renacci. Timken, a manufacturer of bearings, alloy steels and related components, is one of Renacci's top donors. Members of the Timken family, company officials and a company PAC have given at least $210,000 to Renacci in the past two years, according to The Cleveland Plain Dealer.

“Thanks guys. Very important to someone important to us all,” Tom Whatman, the executive director of Team Boehner, wrote after the change was completed.

“In no way do campaign contributions influence how lines are drawn,” Dittoe said.

The redistricting emails included a consideration of partisan advantage down to the level of individual streets.

In an email to Ray DiRossi, one of the two staffers responsible for drawing the state’s maps, a Republican state senator said she knew that another Republican state legislator was “looking for Republicans” in her county and suggested a list of more than 80 streets in 10 neighborhoods where she had received a “good response.”

In September, as the redistricting maps were being approved, the chief of staff for the Republican state house speaker sent DiRossi a list of 43 of the state's legislative districts, ranked according to the total of so-called in-kind contributions made to House races in each district.

According to the Federal Election Commission, "The donation of office machines, furniture, supplies — anything of value — is an in-kind contribution. … A donation of services is also considered an in-kind contribution."

In nine of the districts, in-kind donations totaled more than $2 million over the past decade.

The rankings appeared to be a measure of which districts had been most competitive over the past 10 years, since many of the districts that received the most in-kind contributions had alternated between Republican and Democratic control.

"Ray was running a quick analysis on inking contributions made to house races over the last decade and thought you'd find it interesting which districts were on top," Troy Judy, Ohio House Speaker Batchelder's chief of staff, wrote in an email.

DiRossi wrote back a few minutes later, expressing surprise at the position of two districts on the list. "But we have made significant improvements to many HDs [House districts] on this list. Hopefully saving millions over the coming years," he added.

DiRossi’s comment seemed to suggest that the new maps would be less competitive and thus require fewer campaign donations — a potential savings of millions of dollars.

"It's 1AM—go to bed you political junkies," Heather Mann, another of the state's redistricting staffers, wrote back.

Dittoe said the contribution statistics were sent to several people, and that since the redistricting maps had already been completed by the time the email was sent, the statistics could not have prompted any changes in the maps.

DiRossi and Mann, who is currently a deputy legal counsel in Batchelder’s office, were each paid $105,000 in public money for a few months of redistricting work, according to public documents obtained by the Ohio Campaign for Accountable Redistricting.

Anything said about redistricting by politicians can be used as evidence in a legal challenge of a mapping plan, so politicians are typically warned to keep silent in public about redistricting plans. In a ProPublica interview last week, Georgia Congressman Lynn Westmoreland, a point man for the Republicans' redistricting effort, said congressional delegations were briefed on redistricting protocol and warned that whatever they said could be used in court.

Westmoreland said he also warned members of Congress to work as a team and “not to get greedy.”

“Pigs get fat; hogs get slaughtered,” he said.