For the urban areas, here's what it likely takes to win Ohio:

In recent decades, a reliable rule-of-thumb for any Democratic presidential candidate to win Ohio requires winning Cuyahoga County (Cleveland) by at least 150,000 votes, breaking even in Franklin County (Columbus), and losing Hamilton County (Cincinnati) by no more than 60,000.

The 21 northeastern counties in Ohio comprise 40% of the vote. They tend towards Democrats. (There are three other major urban areas: Lucas (Toledo), Montgomery (Dayton), and Summit (Akron.)

For the rural areas, the Democratic candidate also needs to do well in the Appalachian area of Southeastern Ohio, with its 29 counties, where

.... voters, always angry about chronically high unemployment, are famous for turning out the party in power.

In 1992, Bill Clinton not only beat George H. Bush two to one in Northeastern Ohio, he won a total of 31 out of Ohio's 88 counties. The vote results by county are here (pdf.)He did even better against Bob Dole in 1996. (County vote results here (pdf.)

Bill Clinton won Ohio in 1992 and 1996 by achieving this formula. He won 31 counties in 1992 and defeated George H.W. Bush 2-to-1 in Democratic-dominated northeastern Ohio, whose 21 counties account for about 40 percent of the statewide vote. Clinton was able to minimize Bush’s winning percentage in rural and suburban counties, and in 1996 he improved upon this performance against Republican Bob Dole.

Gore and Kerry were not able to match Clinton's numbers in the rural areas. As to Kerry,

In 2004, Kerry shattered those benchmarks, but still lost to Bush. It can be argued that Kerry maximized the Democratic vote in the state; he won Ohio’s big six urban counties, which accounted for 42.7 percent of the statewide vote, by 14 percentage points, 57-43.

But Bush more than made up the difference in the growing suburban counties and rural counties. Bush not only equaled his 2000 performance by carrying 72 of 88 counties, he improved it by increasing his vote take in 78 counties. As Kerry was racking up big margins in the big six urban counties – which also include Lucas (Toledo), Montgomery (Dayton), and Summit (Akron) – Bush more than matched that performance by winning 57 percent of the total votes in the other 82 counties, which accounted for 57.5 percent of the Ohio vote.

So, what's the message here? Maybe that if Barack Obama is the Democratic nominee, he is unlikely to win Ohio in November unless he can also carry the rural counties against John McCain. And if he doesn't win Ohio against John McCain, he's unlikely to win the Presidency.