Every 10 years, after a US census count, a panel at the Ohio State House gets examine and redraw the lines for each of Ohio's 16 districts for the US House members.
Whichever political party is in control of the Ohio house at the time of the census, gets to appoint the panel.
In 2010 the Republicans had more members at the Ohio House meaning they got to set the new lines for the years 2012 through 2022.
The fear is when one political party is in control of the process they may take advantage and draw the lines in a way that helps their party, which is a move called gerrymandering. This whole process is explained very well by Ballotpedia.
After the 2012 redistricting here's how Ohio's 16 districts laid out.
But here is how it looked from 2011 through 2013.
The biggest changes come when district nine was allowed to stretch all the way into Cleveland's west side which would be considered a Republican lean. That being said Democrat Marcy Kaptur has had a strong hold that district because of her ties to the Toledo area.
District 16, Renacci's district, is also allowed to stretch all the way from Akron into southern and far western Cuyahoga County which would also be a Republican lean.