A chart showing a fascinating historical perspective of the current housing crisis.
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It would probably be more reliable to predict the bottom by looking at the ratio of house prices to income. That shouldn't change too fast.
Most places, the cheaper houses are new developments on the city's fringe. Since a lot of people live there, you need to take them into account when looking at 'housing costs.' But you don't take into account new developments when looking at real estate as an asset. You're not buying 'housing' your buying 'houses.'
Existing properties can increase while cheap new houses keep averages down.
As for existing houses becoming more central, I tend to disagree that this is inevitable. Many suburban and exurban houses are going to be abandoned as oil becomes scarce. Many towns and locations have died instead of developing. We tend to assume that existing houses will age well, but this is driven by survivor bias as we forget about those that are abandoned and die.
As for the long-term influence of population trends, if the population continues to grow, it will be too large for the planet's resources long before we run out of physical space.
Central Rome has been a more or less desirable place to live for more than 2000 years, modulo the odd barbarian invasion, plague, war, etc... Even the places that have waned in importance with time still usually have expensive city centers that aren't bad places to live.
> Chicago and San Francisco weren't even on the map two centuries ago.
But now that the tabula is no longer rasa, those locations are likely to be sought after - maybe more, maybe less over time, but over the long run, they'll attract people.
My point is that housing technology is nothing compared to demand for good locations in terms of its affect on prices, and good locations have a lot of staying power.
BTW, those marshy areas in Lazio have been fairly marginal for a long time:
There are many, many more desirable places to live now in the US than there were 50, or 100 years ago. While desirability is subjective, I'd argue that the growth in the number of desirable places to live is outpacing population growth. The revitalization of many American downtowns, as well as the necessary reorganization of our land use, will further propel this trend.