The mayor of Brisbane, a small city squeezed between San Francisco and Silicon Valley, shares at least one thing with many of her constituents: she can't afford a home of her own. The fact that Mayor Madison Davis lives with her parents highlights the broader affordable housing crisis afflicting the US.

It’s not just places like the San Francisco Bay Area that have become difficult for the less-than-wealthy to call home. According to Out of Reach, a report published by the National Low Income Housing Coalition (NLIHC), a person earning minimum wage and working a 40-hour week can afford a one-bedroom home at fair market rent in just 22 of the country’s more than 3,000 counties.

The World Economic Forum has used data published by the NLIHC over the years to create a visualisation of the evolution of the US affordable housing crisis since 2005. Even a place one might think of as affordable, like North Dakota, requires someone earning minimum wage to work 91 hours per week - more than half of the total hours in a week - to afford a two-bedroom place at fair market rent. In the most expensive locales, there are literally not enough hours in a week to make this feasible.

Many counties, many colours

The visualisation uses colours to signify the hours required per week at a minimum-wage job in order to afford a two-bedroom home at fair market rent in each US county. The range starts with blue, which marks the low end of 46.62 hours per week, then progresses upward through light blue, green, tan, orange, and then finally red - which marks the high end of 221.1 hours (important to note: there are just 168 hours in a week). The colours fluctuate as the years roll by.

In the relatively affluent suburbs of Washington DC, the change over time is from tan to red—while the urban area of DC itself progresses from tan to green.

What’s going on?

As the cost of housing has increased, wages in the US have stagnated. When accounting for inflation, the real average wage in the country now has about the same amount of purchasing power as it did 40 years ago, according to data published by the Pew Research Center. What wage gains have been realised have been mostly enjoyed by the highest earners, according to the data; since 2000, usual weekly wages have risen by 15.7% for the top-tenth of earners, and by just 3% for the bottom tenth. Meanwhile federal housing assistance programs are chronically underfunded, according to the Urban Institute.

The usual suspects

In California, the number of weekly hours required at a minimum-wage job in order to afford a two-bedroom apartment is a daunting 119. In San Francisco (which is both a city and a county), that figure jumps to 218 hours. If anything, things may only get worse for the less affluent in San Francisco. The impending initial public offerings for Uber, Airbnb and Pinterest, all located in the area, will likely create thousands of new millionaires eager to upgrade their abode and push the average cost of housing higher.

King County, home to Seattle, only progresses from green to nearly tan in the visualisation. That’s a pale reflection of more dramatic change within the Seattle area, home to Amazon, where a minimum-wage earner now needs to hold 3.1 full-time jobs to afford a two-bedroom home, according to the NLIHC.

Places you may not suspect

Relatively expensive housing pervades the US in areas well-removed from the typical hot spots. Pulaski County in Arkansas never becomes more affordable than green throughout the visualisation, for example. While Arkansas has the cheapest housing of any state in the US, according to the NLIHC, a person there must nonetheless work 65 hours a week earning minimum wage to afford a two-bedroom place at fair market rent.

The Detroit area, where the unemployment rate spiked to nearly 20% after the 2008 financial crisis, is another case where the county-based visualisation provides just a glimpse of dramatic change within - a surrounding Wayne County, Michigan only slips from tan to a more affordable light green over the years. Still, even as Wayne County has become more affordable, on a statewide basis a person in Michigan must nonetheless work 73 hours per week earning minimum wage in order to afford a two-bedroom home.