When I lived in London, I was always impressed that there were "projects" in neighborhoods like Chelsea (possibly the most affluent in all of the UK). After no

When I lived in London, I was always impressed that there were "projects" in neighborhoods like Chelsea (possibly the most affluent in all of the UK). After noticing that striking example, I've begun to see that pattern (although more subtly) in a lot of cities, including my own (Madrid, Spain). I'm all for building affordable housing, but it seems to me that the idea of building affordable housing close more premium housing has been around for some time, and I'm not really sure what it has accomplished for anyone. Are there examples of success in doing this, and what can be learnt from past failures?