global mapping of urbanization
OverviewAlthough cities cover a tiny fraction (< 1%) of the world’s surface, urban areas are the nexus of human activity with >50% of the population and 70-90% of economic activity. As such, material / energy consumption, air pollution, and expanding impervious surface are all concentrated in urban areas, with important environmental implications at local, regional and potentially global scales. New ways to measure the built environment over large areas are thus critical to answering a wide range of research questions on the role of urbanization in climate, biogeochemistry and hydrological cycles. In this ongoing research initiative, we have developed a new dataset depicting global urban land c. 2001 based on Moderate Resolution Imaging Spectroradiometer (MODIS) 500m data. Our methods exploit temporal and spectral information in one year of MODIS observations, classified using an ensemble decision tree classification approach. Our results show a mean overall accuracy of 93 percent at the pixel level and a high level of agreement at the city scale (R2 = 0.90). This map has been downloaded more than 1500 times for use in research and private sector activities, and has been recently described as ‘the global standard’ for depicting global urban extent.
With new NASA funding (2014), our recent efforts have focused on: (1) monitoring urban expansion globally, 2000-2010 (includes development of new c. 2000 and c. 2010 urban extent datasets); (2) providing sub-pixel estimates of global urban land use; and (3) differentiating downtown areas from low density residential land. The preliminary results for (1), monitoring urban expansion, are available for East and Southeast Asia.
Mertes, C.M., Schneider, A., Tan, B., Sulla-Menashe, D., Tatem, A.J. (2015). Detecting change in urban areas at continental scales with MODIS data. Remote Sensing of Environment, vol. 158, pages 331-347.
Huang, X., Schneider, A., Friedl, M. (2015). Mapping fractional urban cover in China using MODIS time series and DMSP/OLS nighttime lights. Remote Sensing of Environment, in review.
Schneider, A. (2012). Monitoring land cover change in urban and peri-urban areas using dense time stacks of Landsat satellite data and a data mining approach. Remote Sensing of Environment, vol. 124, pages 689-704.
Schneider, A., Friedl, M.A., Potere, D. (2010) Mapping urban areas globally using MODIS 500m data: New methods and datasets based on urban ecoregions. Remote Sensing of Environment, vol. 114, p. 1733-1746.
Friedl, M.A., Sulla-Menashe, D., Tan, B., Schneider, A., Ramankutty, N., Sibley, A. (2010) MODIS Collection 5 Global Land Cover: algorithm refinements and characterization of new datasets. Remote Sensing of Environment, vol. 114, p. 168-182.
Schneider, A., Friedl, M.A., Potere, D. (2009). A new map of global urban extent from MODIS data. Environmental Research Letters, vol. 4, article 044003.
Potere, D., Schneider, A., Angel, S., Civco, D. (2009). Mapping urban areas on a global scale: which of the eight maps available is more accurate? International Journal of Remote Sensing, vol. 30, p. 6531-6558.
Click here for additional publication information.
To download the new map of MODIS 500m global urban extent in a variety of formats and projections, click here.
What will the global urban landscape look like in the future?
Annemarie Schneider, Carly Mertes, Jo Horton, James Rollo, Ian Schelly