A new global map of urban areas shows that cities occupy less than 0.5% of the world's total land area. Growing populations and increased rural-to-urban migration in developing countries mean that over 50% of the global population now live in urban areas. Locally, cities have a considerable impact on the environment: they create microclimates (such as the urban heat island effect), pollute water and air, destruct natural habitats with a consequent loss of biodiversity and degrade soil. These influences can extend to regional and possibly global scales, for example, through the transport of air pollutants in the atmosphere. The new map reveals that previous global urban maps may have over-estimated the extent of built-up areas. This map estimates the total urban land footprint as less than 0.5% of the world's total land area. There are variations between continents: urban land areas in Africa cover 0.17% of the continent, 0.67% in North America, 0.47% in South America and 0.53% in Asia. Urban land extent in Europe is higher than the average at 1.78%, reflecting the extent of the built environment. The accuracy of the map was assessed by comparing the global map with very detailed local maps of urban areas compiled from high resolution independent data for 140 randomly chosen cities. Compared with the other global mapping systems, this map has the highest overall accuracy of 93%.