Hacker News

Anne Hidalgo, the mayor of Paris, is usually credited for it. It works in Paris because the official boundary is quite small compared to other cities, about 100km^2 containing 2 million people, whereas in Berlin the equivalent is almost 900km^2 and 3.5 million people. So the population that vote for her are almost exclusively urban dwellers whereas in Berlin the mayor has to appease suburbanites too.