In 1954, San Francisco ran out of large, vacant land tracts to build on. The city realized it was in a housing crisis in 1966, launching a Housing Report that year which continues to this day.

Eric Fischer, a former Google employee who is now the artist in residence at the Exploratorium, studied the trajectory we've been on since then, essentially by archiving 68 years of newspaper housing ads. That's all on his blog, Experimental Geography, where Fischer puts one of his goals like this: "To understand what causes high housing costs, we must first have an idea of how high costs are, and how high they have been over time."

Fischer, who has been praised by Curbed and others, found that prices were going down during the 1940s. Rents then stabilized in 1954, and in 1956 began a steady, 60-year climb that continues to 2016. He explains his central methodology like this:

"[For] each first Sunday in April from 1948 through 1979, plus a few other years, I made a list of all the advertised unfurnished apartments, flats, houses, and, later, condos, regardless of size, that were advertised in the Chronicle. Mostly I used the San Francisco Public Library's page scans of the newspaper but resorted to microfilm for the few later years where no page scans are available."

According to those listings, and with the addition of Craigslist and other web data in the years where that was available, Fischer found that the steady increase in median rent has figured at about 6.6 percent every year. Accounting for inflation, rents have gone up 2.5 percent per year, and have quadrupled in effective cost over those six decades. "It is still an alarming increase," writes Fischer.

There are exceptions and deviations to this chart of the median city rent. Why was rent high in 1998 and low in 2005? Fischer doesn't claim to know. But moving forward and adding variables is where it gets pretty interesting. As the Observer, who loved the project, breaks down those variables, they are:

1. The number of jobs located in San Francisco County. 2. The number of places in San Francisco County for people to live. 3. The total amount of money that's paid to everyone who works jobs in San Francisco County.

In the end, Fischer argues that lower salaries, lower employment, and more housing construction make for lower rents. As the Observer summarizes it: "this would mean the way to make San Francisco as affordable as (say) Portland would be to either cut everybody’s salary in half, or fire half of them, or allow the city's population to rapidly grow about 50 percent, to about 1.2 million, while the number of housing units increased even faster."

So what can San Francisco change to make rents lower, according to Fischer's thinking? Going back to 1981, for example, isn't possible.

His conclusion is modest. "The city and its citizens should try to increase the housing supply by an average of 1.5% per year (which is about 3.75 times the general rate since 1975, and with the current inventory would mean 5700 units per year)" because otherwise "prices will probably continue to rise uncontrollably."

All of Fischer's data is on Github, where you can toy with it yourself.

Related: Report: San Francisco Rents To Skyrocket 10.5% By Year's End