The Joint Research Centre (JRC) has released what it is calling “the largest and most comprehensive database on cities ever published”. It has launched its Global Human Settlement Layer (GHSL), a tool with data on all 10,000 urban centres across the globe. Through use of this tool, researchers have discovered that the world has become even more urbanised than previously thought.
For example, the data shows that populations in urban areas doubled in Africa and grew by 1.1 billion in Asia between 1990 and 2015.
Globally, more than 400 cities have a population between 1 and 5 million. More than 40 cities have 5 to 10 million people, and there are 32 'megacities' with above 10 million inhabitants.
There are some promising signs for the environment: Cities became 25 percent greener between 2000 and 2015. And although air pollution in urban centres was increasing from 1990, between 2000 and 2015 the trend was reversed.
With every high density area of at least 50,000 inhabitants covered, the city centres database shows growth in population and built-up areas over the past 40 years. Environmental factors tracked include:
- 'Greenness': The estimated amount of healthy vegetation in the city centre
- Soil sealing: The covering of the soil surface with materials like concrete and stone, as a result of new buildings, roads and other public and private spaces
- Air pollution: The level of polluting particles such as PM2.5 in the air
- Vicinity to protected areas: The percentage of natural protected space within 30km distance from the city centre's border
- Disaster risk-related exposure of population and buildings in low-lying areas and on steep slopes.
The data is free to access and open to everyone. It applies big data analytics and a global, people-based definition of cities, providing support to monitor global urbanisation and the 2030 Sustainable Development Agenda.
The information gained from the GHSL is used to map out population density and settlement maps. Satellite, census and local geographic information are used to create the maps.