Nearly two-thirds of the homes in the city of San Francisco today are worth more than a million dollars, according to the real estate site Trulia that tracks home values. That dizzying number speaks to the city's affordable housing crisis — a crisis that has officials fretting about housing even for families making $140,000 a year — and the breakneck pace at which it's getting worse. The number of million-dollar properties, according to Trulia economist Ralph McLaughlin, has more than doubled in the city since just 2010.

These numbers, though, don't convey the rise and spread of out-of-reach real estate quite like the below animation does. This map from Trulia tracks the methodical advance of million-dollar homes from the San Francisco neighborhoods where they've long been common to parts of the city that are newly becoming inaccessible. In some neighborhoods where a small fraction of homes five years ago were worth a million, a majority are today. These red dots represent homes that Trulia has valued at seven figures or more, not necessarily homes that have sold at that price:

That picture captures what long-time residents no doubt experience as an advancing threat with its own front lines (the blood-red visual certainly aids the impression of a contagion). And in the next five years? There's not a lot of city left, especially in this city that has long struggled to expand as the demand to live there has.