Public housing estates have come to define the modern urban landscape of Hong Kong. There are a mix of older and newer units which cover a broad range of architectural styles and layouts all designed with a common aim: to provide housing and basic social infrastructure for as many people as possible in a relatively small, densely populated urban space. Each estate functions almost as a small city within a city, with many featuring shops, restaurants, fitness centers, doctor’s offices and schools; Some even have dedicated post offices and metro stations. Hong Kong is one of the most densely populated urban centres in the world (57,250 persons per square kilometre in the most densely populated area) and there are hundreds of public housing estates in the city, the largest of which can house up to 36,000 people. Around one-third of the population of Hong Kong live in public housing apartment blocks.