This description pertains to the primary download. Details on revised (newer) versions of the datasets are listed below under Additional Files. -- Two global maps (raster files) of tree density. These maps highlight how the number of trees varies across the world. One map was generated using biome-level models of tree density, and applied at the biome scale. The other map was generated using ecoregion-level models of tree density, and applied at the ecoregion scale. For this reason, transitions between biomes or between ecoregions may be unrealistically harsh, but large-scale estimates are robust (see Crowther et al. 2015). At the outset, this study was intended to generate reliable estimates at broad spatial scales, which inherently comes at the cost of fine-scale precision. For this reason, country-scale (or larger) estimates are generally more robust than individual pixel-level estimates. These two maps initially appeared in Crowther et al. (2015), with the biome map being featured more prominently. As they are produced, updated versions of these datasets, as well as alternative formats, will be made available under Additional Files.