Density – the number of people living in a given area, usually expressed as people per square kilometre – is at the centre of public debate on the future growth of cities. Used as a planning tool, awareness of density can help to curtail over-development and overcrowding, or ensure that scarce urban land is not under-used, especially in areas with good public transport and social amenities. High density does not mean high-rise; large numbers of people can be accommodated in five- or six-storey buildings arranged in a compact and efficient manner, creating congenial places for living.
Good design can produce desirable neighbourhoods in cities across the world by balancing dense development with access to open space and good transport. Dense urban environments can create sustainable cities; more dispersed developments use up more land and need more infrastructure – water, gas, electricity, roads – with negative impacts on the environment. High density housing can be associated with poverty and overcrowding, especially in the slums of developing countries. However, good design can produce desirable neighbourhoods in cities across the world by balancing dense development with access to open space and good transport – as evident in some of the most successful neighbourhoods in London, Paris and New York.
The four models shown in this section compare, at the same scale, the number of people living within the administrative boundaries of four of the ten cities featured in the exhibition. The peaks show the highest residential densities, with the largest number of people concentrated in a square kilometre. They range from the high-density of Cairo and Mumbai to the more dispersed, but bounded London (contained by the Green Belt) and the sprawling Mexico City.