Yes, the housing policies are notoriously stupid, but there are parameters under which they are inconsequential. What are they? If there had been no change in

Yes, the housing policies are notoriously stupid, but there are parameters under which they are inconsequential. What are they? If there had been no change in demand it all, San Francisco housing policies would not have been a problem. That was not a robust assumption given internal freedom of movement within the United States. And while San Francisco has put its own delightful spin on it, gentrification is by no means unique to the Bay Area. Neighborhoods shift over time inevitably but sometimes these shifts are sudden and many former and soon to be former residents feel pushed out and left out. What are the parameters for a neighborhood population to turn over without anyone noticing or caring? Maybe it depends somewhat on the nature of the new residents. If they are moving for a new job, new building can blunt the impact. People will take the new housing that is within a credible commute distance of work. If, however, the new residents are deliberately seeking to enter and bid up historic or trendy areas, some kind of defense is necessary as well. In Berlin's case, there was legislation to prevent too much improvement of apartments -- putting in new kitchens and so forth -- in certain areas, to prevent the rent from rising. San Francisco has new residents of both types; and suffers from many other forces. It is small and on a peninsula, so there is only one dimension for growth (Berlin, DC and similar areas can grow square-wise). Its housing policies prevent new building. Public transit is not that great; getting to work from the western half of the city takes almost as long as coming from Oakland. Thousands upon thousands of people moved here to take jobs in the area. Many of them targeted small neighborhoods like The Mission and Noe Valley and Potrero Hill. The latter behavior is particularly remarkable in SF because these neighborhoods were typically far from their jobs. Company shuttles undoubtedly contributed to this problem. It was like public transit operating in reverse: centralizing the residences and dispersing the commercial centers.