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The median house price in Pittsburgh is $140,500, and a potential buyer for a median-priced home in the city would need to earn $32,390 annually. In San Francisco, the median home price is $885,600 and a buyer would need an annual income of $161,947.60 in order to buy.

The differences in affordability reflect a couple of major issues: availability of houses to buy and employment opportunities. Rust belt cities like Pittsburgh, Cleveland and Cincinnati — the three most affordable cities — do not compete on salaries with the three least affordable cities, all of which are on the west coast: San Francisco, San Diego and Los Angeles.

And housing inventories are higher: Pittsburgh had more than 10,000 listings at the end of May, according to Realtor.com, nearly twice as many as the San Francisco metro area. Cleveland had nearly 11,000 properties listed for sale, compared with about 6,900 in the San Diego area. Third-most affordable, Cincinnati, had over 9,000 listings, compared with nearly 25,000 in Los Angeles, but the Los Angeles metro area has nearly 13 million residents, compared with just over 2 million in Cincinnati.

The data come from a recent report by HSH.com, which claims to be the nation’s largest publisher of mortgage and consumer loan information. The researchers compared first-quarter mortgage interest rates and home prices with second-quarter rates and prices as well.

To create its ranking, HSH.com used the National Association of Realtors’ second-quarter data for median home prices and its own second-quarter data for mortgage rates. The researchers then calculated the income needed to purchase a median-priced home based on the monthly payment for principal, interest, taxes and insurance after a 20% down payment. The firm also used the standard 28% “front-end” debt ratios.

The national averages for the second quarter were a mortgage interest rate of 3.73%, a median home price of $240,700, a monthly payment of $1,229.65 and a salary of $52,699.17. The median income in the United States is about $52,000.

Here are the top five most affordable metro areas:

1. Pittsburgh: 3.62% mortgage rate; $140,500 home price; $755.77 monthly; $32,390 annual salary
2. Cleveland: 3.72%; $138,100; $803.46; $34,434
3. Cincinnati: 3.79%; $160,600; $867.51; $37,179
4. St. Louis: 3.70%; $170,300; $889.73; $38,131
5. Detroit: 3.78%; $164,200; $899.31; $38,541

The five least affordable metro areas are:

1. San Francisco: 3.77% mortgage rate; $885,600 home price; $3,778.78 monthly; $161,948 annual salary
2. San Diego: 3.84%; $589,900; $2,553.62; $109,441
3. Los Angeles: 3.74%; $480,000; $2,148.81; $92,092
4. Boston: 3.67%; $435,800; $2,042.99; $87,557
5. New York City: 3.70%; $395,400; $2,011.69; $86,215

Here’s a map from HSH.com showing salaries needed to buy a house in 27 U.S. cities.

Mortgage rates fell in all 27 metro areas in the HSH.com survey, while more affordable housing showed up in just three cities: Tampa, Orlando and Miami, Florida.