There are two types of maps available: Choropleth (maps where polygons are shaded to depict the amount of a resource) and Raster (maps where each pixel is shaded to indicate amounts).
The choropleth Northern Forest Resource Maps are shaded to summarize forest resource information for each county. The choropleth Forest Volume and Species Distribution maps were constructed using a circle moved systematically over the region to "paint" forest estimates on a forest/non-forest map.
The raster maps of Species Basal Area depict amount and distribution of per-species basal area (cross sectional stem area) for each 250-m pixel in the eastern half of the contiguous 48 states. They were produced from FIA plot data using a multivariate statistical procedure called gradient nearest neighbor imputation.
The Species Basal Area Maps are presented in a beta version of our map atlas web mapping tool.
Last Modified: 05/20/2011