Section 5: Google Earth Data for the Universe of 3,646 Cities

In recent years various academic, governmental, and commercial groups have created no fewer than eight global maps and two related maps of the built environment, most of them at a relatively coarse resolution with pixel sizes of 250 - 1,000-meters. These maps identify impervious surfaces - pavements, roofs and compacted soils - that are closely associated with the built environment. It has been quite difficult to tell how accurate these eight maps are. Individual map estimates of the total area of built environment in the world vary by as much as an order of magnitude: from 276,000 km² in Vector Map Level 0 (VMAP0) to 3.532 million km² in the Global Rural-Urban Mapping Project (GRUMP).

Potere et al (2009) set out to test the accuracy of these global maps with a two-tier assessment. The first-tier assessment compared these maps with a set of 30-meter-resolution maps of cities based on Landsat imagery. The second-tier assessment tested the Landsat-based maps for accuracy with 10,000 Google Earth validation sites. The central conclusion of their paper is as follows: "Among the eight maps examined for accuracy, the Mod500 map was found to be the most accurate by all three accuracy measures employed" (Potere et al, 6553). Our estimates of urban land cover in the universe of cities, as well as our projections, are therefore based on this Mod500 map. To the best of our knowledge, this map provides the most complete, most reliable, and the most realistic estimates of urban land cover on a global scale at the present time. We refined the Mod500 map to include 311 new urban clusters for large cities that had no corresponding clusters, but we did not change any of the clusters found on that map.

As a result, we now have a global map on a Google Earth platform of urban clusters with a 463-meter pixel size that are associated with a total of 3,646 named large cities and metropolitan areas in all countries. These cities had a total population of 2.01 billion people in 2000, and these population estimates came, for the most part, from Thomas Brinkhoff's City Population Web site (Brinkhoff, 2010). The estimates are associated with the name of the city or metropolitan agglomeration, but are not populations within a well-defined administrative boundary. According to our calculations, the urban clusters associated with large cities had a total built-up area of some 340,000 km² in the year 2000. Their locations are shown in the map below. A detailed description of the way this universe of cities was constructed and refined is given in Angel et al. A Planet of Cities: Country Estimates and Projections of Urban Land Cover, 2000-2050.

The Nine World Regions and the Universe of 3,646 Cities, 2000

To download this file, you must first download Google Earth. The download is available free of charge at the Google Earth Web site.

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Download zipped kml files containing the urban land cover for 3,646 large cities, in the year 2000. These files can only be viewed in Google Earth.

Download Excel spreadsheet containing data for 3,646 large cities, in the year 2000.