It is hard to overstate just how quickly the people of this planet have decided to embrace city living. In 1800 just 2% of the world's population lived in cities, while in the 1950s one-third of us lived in cities, but today more than half of us do. Every week around 1.5m people join the urban population, through a combination of migration and childbirth and by 2050 only one-third of the global population will still be living in rural areas, while more than 6bn of us embrace the traffic, smog, crime and higher cost of living.

The bizarre thing is that nearly every survey on rural/city living produces the same results…people are happier living in rural areas. What is even more worrying, considering the growth trend for most city populations, is that the least happy city dwellers are those that live in the most densely populated city boroughs, while the happiest are those living in less densely populated rural/suburban towns that can still have relatively quick access to a large city.

Another 40-year study in the US, published in the journal Cities, discovered that large cities are far less happy than smaller ones. The study found that unhappiness intensifies when a city's population reaches 'hundreds of thousands'. The study concluded that 'a person does not have to give up city living to be happy she just needs to avoid the biggest cities.'

So why do people continue to move to large cities? Whether you move to a city to go to a better university, to find a job or because you are just bored and looking for excitement, the reality is that not everyone can find a better life there. There have to be winners and losers. For example, in the US income inequality in the 50 biggest cities is 20% higher than the national average. However, globally, especially in poor countries like India and Nigeria, when a person moves to a big city like Mumbai or Lagos they often end up living in a slum. Since 1990, the number of people globally living in urban slums has increased by 33%.

Between now and 2050, 90% of the expected increase in the world's urban population will take place in the urban areas of Africa and Asia. A solution needs to be found immediately to house the people that are already living in urban slums, not to mention the 70-80m people that move to a city every year.