The data have been aggregated such that dots are placed by hydrologic units within each state. The data have been masked and dots do not appear on areas determined to be 95 percent or more Federal land. Data for Puerto Rico and the U.S. Virgin Islands are aggregated by 6-digit hydrologic unit. NRI maps reflect national patterns rather than site- specific information. No data are collected for any year that land is in this ownership.
Land cover is the vegetation or other kind of material that covers the land surface.
A geographic entity, defined by the Federal OMB for use by Federal statistical agencies, based on the concept of a core area with a large population nucleus, plus adjacent communities having a high degree of economic and social integration with that core. Additional outlying counties qualify to be included in the MSA by meeting certain other criteria of metropolitan character, such as a specified minimum population density or percentage of the population that is urban. MSA's in New England are defined in terms of cities and towns, following rules concerning commuting and population density. MSA's were first defined and effective June 30, 1993. Also included are tracts of less than 10 acres that do not meet the above definition but are completely surrounded by Urban and Built-up land.