Urban Clusters

The Global Urban Footprint maps human settlements worldwide with unprecedented spatial resolution of 0.4 arcsec (about 12 metres), allowing the analysis of urban patterns and structures.
Source: GUF.

Urban populations grow detached from their remote impact on the environment

Spurred by the increasing dominance of global urbanisation, there have been initiatives to map urban areas in detail at the global scale:
The recently published Atlas of the Human Planet 2016, offers a comprehensive view of urbanisation dynamics, spatial maps and summaries quantifying the growth of the global urbanised population over the past 40 years, covering the period from 1975 to 2015. It is based on the Global Human Settlement Layer (GHSL), a collection of maps of the human presence and built-up areas, from villages to mega-cities, derived from satellite data with a 38 m detail. Focusing on the current status of settlements, the “Global Urban Footprint” (GUF) provides detailed worldwide mapping of built-up settlements with a spatial resolution of around 12 m – examples are shown throughout this atlas.
Some extraordinary changes have occurred across the globe over the past 40 years with regard to human habitation; the Atlas of the Human Planet 2016 illustrates the following findings:

  • Globally, built-up areas increased by approximately 250 %, while population increased by a factor of 1.8;
  • There is significant geographical variation in population growth and built-up areas. The largest population growth was observed in low-income countries where, for example, the population of Africa tripled and its built-up area quadrupled. In contrast, the population of Europe was stable but its built up area doubled;
  • Urban Centres: Most of the world’s population live in agglomerations with densities greater than 1 500 people per km2 and more than 50 000 total inhabitants. As of 2015, 13 000 individual Urban Centres existed on the planet;
  • Urban Clusters: Clusters of agglomerations with more than 300 people per km2 and at least 5 000 inhabitants per km2, were used to capture both the dense Urban Centres and the surrounding suburbs and towns. In the past 40 years, the number of these Urban Clusters have doubled. Urban Clusters constituted 4 % of the terrestrial land mass in 1975. By 2015, this figure rose to 7.6 %, which is approximately half the size of the European Union;
  • About 85 % of the planet’s inhabitants live in cities, either in Urban Clusters and Urban Centres.

The impacts of urbanisation on the environment are immediate and profound. As urban clusters expand, productive land and soil is sealed, and natural ecosystems (e.g. pastures, forests) are replaced to varying degrees by land use to support urban centres. This includes agricultural fields, pens and pastures for animals, housing for workers and the inevitable complex network of pathways, roads and railways that connects it all5. The ebb and flow of commodities, services and people into and out of urban/non-urban regions (such as ecosystem services (water, food), the physical transport of materials (mining of raw materials to construct the built environment), people (migration, tourism and lifestyle mobility), money (remittances) and so forth) affect the populations, economies and status, development and management of distant lands far-removed from any particular urban environment.

Dynamics in built-up areas
Source GHSL.

Distribution of global population in Urban Centres, Urban Clusters and rural settlements in 2015. About 85 % of global inhabitants live in cities, in Urban Clusters and Urban Centres.
Source: P. Martino et al.

One view of a Beijing skyline shows the encroachment of a rapidly expanding dense urban area into surrounding green areas.
Source: Liniger H.P., 2016.