Global Ecological Land Units (ELUs)

In its first global effort the USGS developed a rich, spatially explicit database of global Ecological Land Units (ELUs) based on the geospatial combination of four global input layers - bioclimate, landform, lithology, and land cover – reconciled into a standard 250-meter raster framework. The bioclimates layer was a modified version of the Global Environmental Stratification (GEnS) dataset produced by Metzger in another GEOSS-commissioned effort. Since no DEM-derived global landforms layer existed, one was initially generated using the Missouri Resource Assessment Partnership (MoRAP) methodology applied to global 250-meter DEM data. The MoRAP algorithm, which uses slope and relative relief parameters, was subsequently improved with the addition of a profile parameter that improved the delineation of tablelands. The lithology layer was the Global Lithology Map (GLiM) that identifies 16 lithological classes at its most general level of classification. For the global land cover, the GlobCover 2009 product, collaboratively produced by the European Space Agency (ESA) and the Université Catholique de Louvain, was initially used. That product was then upgraded by the ESA to a Global Land Cover data layer, which represents the global distribution of 23 land cover classes as interpreted from 300-meter spatial resolution data from the MERIS satellite. The input data (bioclimate region, landform type, surficial lithology, and land cover) was then combined into a single 250-meter raster layer that had 106,959 unique combinations of attribute values. The final product was then produced by generalizing the number of initial attribute classes into a reduced set of 3,639 global ELUs.