"Domus est ubi cor est."

Roman philosopher Pliny the Elder is usually credited with authoring this popular sentiment that "home is where the heart is." But if Pliny were still around today, he might express it a bit differently: "Puto habens cor impetum," or "I think I'm having a heart attack."

Why? A recent report from Interest.com reveals that, much as we all might love our houses, precious few of us can afford to own one anymore. As a general rule, interest.com suggests that homebuyers spend no more than 28% of monthly income on "total principal, interest, taxes and insurance" on a house. Judged by that standard, according to the Bankrate (NYSE:RATE)subsidiary, in 15 of America's 25 largest cities, housing prices have become downright unaffordable. 

Are you "interested" in knowing which cities?
Interest.com comes to this conclusion by analyzing median income levels in cities from San Francisco, San Diego, and New York (the three least affordable large cities) to St. Louis, Atlanta, and Minneapolis (the three most affordable).

Interest.com then considers the median cost of buying a home there, factoring in home cost and the implied mortgage payments, plus the cost of insuring a home and paying its property taxes. Depending on whether homes cost more than, less than, or just right for what a prospective homebuyer can afford, it assigns each city a letter grade for the "affordability" of its housing market: A to F.

Further clarifying the grades, Interest.com also evaluates how much a city's median income falls short of (or surpasses) its median home price. For example, New York (grade: F) has the third least affordable housing market in the country, with median incomes falling about 32% short of the nearly $400,000 needed to afford a median-priced home.

San Francisco "boasts" the least affordable housing market. This is not so much because wages are low. (To the contrary, your average San Franciscan worker outearns his or her New York counterpart by 21%.) The problem, rather, is that San Franciscan housing prices are no treat at all. The median home price in Frisco: $769,600.

The result, says Interest.com, is that median incomes in San Francisco are barely half what's needed to buy a home there.

Granted, there are still ways to put a roof over your head, even in these expensive cities. Renting rather than owning may be one option (although once tax benefits are factored in, renting is sometimes even more expensive than owning). Landing a job that pays more than the "median" income, or buying a house that costs less than the median -- or both! -- are other ways to make the math work. It's just that, more and more often these days, and in more and more American cities, it's getting harder to make "the numbers" cooperate with people's need to find shelter from the storm. 

Stuck in the middle -- a good place to be
It's not all bad news in Interest.com's report, however. Turn the survey upside down, and you'll find several affordable cities congregating in America's middle states.

Take Chicago, for example. America's third largest city wins only middling marks for affordability -- a C-minus at best. But strong median income levels mean that your average Chicagoan can still almost afford a home. Meanwhile, denizens of fellow Midwestern cities Detroit, St. Louis, and Minneapolis enjoy median incomes anywhere from 14% (Detroit) to 23% (the Twin Cities) higher than what's needed to afford a mid-priced home there.

Homes in Minneapolis, for example, tend to cost barely half what a home will run you in New York City. Yet with a median income of $67,194, Minneapolitans earn $1,400 more than New Yorkers do. Meanwhile, the median wage in Detroit -- $51,857 -- may be a full third lower than what San Franciscans earn. But with a median home price of just $149,000, residents of the Motor City can buy more than five houses for the price of just one home in Cali.

The East Coast -- not as pricey as you might have heard
OK, so for-sale signs in the "flyover" states list lower prices than those on the West Coast do. That's pretty well known. But here's something you may not have heard: Home affordability in states lining the other coast isn't nearly as bad as its reputation might suggest.

In fact, according to Interest.com's data, you can find quite affordable abodes in:

  • Dallas... and Philadelphia, too. Both got graded a "C" for home affordability, but both cities also offer wage levels sufficient to cover the cost of a new home -- $60,482 a year in Philadelphia and $57,398 in Dallas.
  • Phoenix... but also Washington, D.C. Separated widely by geography, these two cities share "C" grades for affordability, and wage levels 7% higher than necessary for home ownership.
  • Both Baltimore and Pittsburgh offer cheaper, C-plus-rated housing markets, plus wage levels more than 10% above the median cost of housing. Turns out, while Pittsburgh's housing market doesn't get as much (bad) press as Detroit's, the median home price in Steel City is actually slightly cheaper than in Motor City -- less than $144,000.
  • Atlanta, too. Graded "B" for affordability, and with strong median income, Atlanta ranks right up there with the Midwestern standouts. Average residents here earn at least 20% more than they need to in order to buy a home there -- which at a median cost of $166,200 is cheap enough to give even Detroit a run for its money.

So don't lose heart, America. Even if 60% of the country's largest cities are now too expensive to live in, it's an awfully big country, and there are lots of places where you can still afford a home.