For centuries humans have huddled together in cities – and it doesn’t look like urbanization is going to slow down anytime soon. There are various reasons why vast numbers of people decide to settle in urban areas, but in the majority of cases it boils down to the simple fact that cities are where the work is. More than half of the world’s population currently lives in urban areas and the United Nations (UN) expects that proportion to increase to 66% by 2050, with close to 90% of the increase concentrated in Asia and Africa.