Last month we wrote about a report from the National Low Income Housing Coalition on how much a worker would have to earn to afford what the Department of Housing and Urban Development considers "fair market rent" in local communities across the country. The government sets these housing rates, which include rent plus utilities, based on the local market for decent-quality apartments of different sizes -- neither dumps nor luxury flats. These are also the rates that HUD uses to establish local housing subsidies.

The National Low Income Housing Coalition took those fair market rents and calculated how much a worker would have to earn per hour to cover such modest housing, if we assume a 40-hour work week and a 52-week year. They call this rate a "housing wage," and it is, unsurprisingly, much higher than the minimum wage in much of the country.

The coalition focused on one person's hourly income that is needed to afford a two-bedroom rental, a scenario that most closely applies to single parents supporting children alone. But they also compiled data on one-bedroom "housing wages" -- a metric that applies more broadly -- and the organization gave us the data at the county level.

We've mapped this more detailed data in the interactive below. This is what you'd need to earn per hour, working a 40-hour week, to cover the kind of housing that the federal government considers modest in your county:

Mapped in finer detail than by state, several geographic patterns are clearer. No single county in America has a one-bedroom housing wage below the federal minimum wage of $7.25 (several counties in Arkansas come in at $7.98).

Coastal and urban counties are among the most expensive. The entire Boston-New York-Washington corridor includes little respite from high housing wages. Marin, San Francisco and San Mateo counties in California rank as the least affordable in the country (scroll over each county in the interactive version for rankings; click to zoom). In each of those counties, a one-bedroom hourly housing wage is $29.83, or the equivalent of 3.7 full-time jobs at the actual minimum wage (or an annual salary of about $62,000). Move inland in California, and housing grows less expensive.

A dark swath of North Dakota that appears to cover the geography of the oil and gas boom stands out as well.

As a commentary on the national minimum-wage debate, this map is limited. While it suggests that a minimum-wage worker can't afford housing in Seattle (where the one-bedroom housing wage is $17.56 an hour), in reality that person probably finds housing by renting a room in someone else's home, by living in the cheapest part of town, or by working considerably more than 40 hours a week. (Remember George W. Bush's praise for the "uniquely American" story of the single mother of three who worked three jobs in Omaha?)

But this map does succinctly portray dramatic variation across the country in housing costs, and it suggests that proposals to modestly raise the minimum wage won't fully solve this problem. While median incomes vary broadly by county, just as housing costs do, the incomes for people who work at the bottom end of any community's wage spectrum do not.

Top ten most expensive counties

State County 1-br. housing wage California Marin $29.83 California San Francisco $29.83 California San Mateo $29.83 Hawaii Honolulu $26.58 Massachusetts Nantucket $25.83 California Orange $25.23 New York Nassau $25.17 New York Suffolk $25.17 California Santa Clara $24.87 California Alameda $24.13

Thirty counties in Arkansas are all tied for the honor of least expensive housing wage, at $7.98 an hour: Ashley County, Boone County, Bradley County, Calhoun County, Clay County, Columbia County, Desha County, Drew County, Franklin County, Fulton County, Howard County, Izard County, Jackson County, Lafayette County, Lawrence County, Logan County, Marion County, Mississippi County, Monroe County, Montgomery County, Nevada County, Newton County, Phillips County, Randolph County, Scott County, Searcy County, Sharp County, Stone County, Woodruff County and Yell County.

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