Equal Area for Land Use Land Cover


RLCM projection blocks
RLCM projection blocks (Cotillon and Mathis, 2017)

With an area close to eight million square kilometers (km), the West Africa Land Use Land Cover (LULC) Project covers a large region, over a fourth of the Continent. Since the LULC data was derived using a sampling approach and completed at a 2 km resolution, it was important that the physical area be equally represented.  To represent LULC spatial data equally, the Lambert Azimuthal Equal-Area Projection was chosen because its main function as a projection is to maintain equal area over large regions (Snyder, 1987).  When the project initially started, and during the initial development of the Rapid Land Cover Mapper (RLCM) (Cotillon and Mathis, 2017) the focus was only on West Africa, so to improve the equal area properties of the projection the system parameters were modified. It was originally based on USGS's Africa standard parameters for the Hydro1K products (USGS, 2017; Steinwand, 1995), specifically a Longitude of Origin of 20 degrees east and Latitude of Origin of 5 degrees north. The original parameters were changed to 3 degrees east and 11 degrees north, thereby decreasing the distance from the map center and improving area properties for the West Africa region (Snyder, 1987).

As a result of the RLCM's initial success in West Africa, it was requested the tool be adapted to be used around the globe and not just tied to West Africa.  To allow for global use the tool was redesigned to use Lambert Azimuthal projections based on the USGS's Hydro1K continental projections (Steinwand, 1995; Cotillon and Mathis, 2017) (RLCM projection blocks figure). The West Africa region is an exception to this because the modified projection was used when the LULC maps were prepared.


Cotillon, S.E., and Mathis, M.L., 2017, Mapping land cover through time with the Rapid Land Cover Mapper—Documentation and user manual: U.S. Geological Survey Open File Report 2017–1012, 23 p., https://doi.org/10.3133/ofr20171012.

Snyder, J. P., 1987, Map Projections – A working manual: U.S. Geological Survey Bulletin 1532 – 383 p. also at https://pubs.er.usgs.gov/publication/pp1395

Steinwand, D.R., Hutchinson, J.A., and Snyder, J.P. ,1995, Map projections for global and continental data sets and an analysis of pixel distortion caused by reprojection: Photogrammetric Engineering and Remote Sensing, v. 61, p. 1,487-1,497. also at http://www.geog.ucsb.edu/~kclarke/Geography128/Steinwand_etal_1995.pdf

U.S. Geological Survey (USGS), 2017, HYDRO1k Documentation ReadMe U.S. Geological Survey, accessed March 2, 2017, at https://lta.cr.usgs.gov/HYDRO1KReadMe