About the Data
Estimates presented here are based upon the latest information from the
National Resources Inventory (NRI).
The NRI is a longitudinal sample
survey based upon scientific statistical
principles and procedures. It is conducted by the U.S. Department of Agriculture’s Natural
Resources Conservation Service (NRCS),
in cooperation with Iowa State University’s Center for Survey Statistics and Methodology.
These results are based upon the 2012 NRI, which provides nationally consistent
data for the 30-year period 1982–2012.
Current estimates cover the contiguous 48 States, Hawaii, and the Caribbean Area.
Release of NRI results is guided by NRCS policy and is in accordance with OMB
and USDA Quality of Information Guidelines developed in 2001.
NRCS is releasing NRI estimates only when they meet statistical standards and are scientifically
credible in accordance with these policies;
also, measures of statistical uncertainty are provided for all 2012 NRI estimates released to
The findings on land use come from the NRI data category "Land Cover/Use,"
which comprises mutually exclusive categories such as cropland, rangeland, forest land,
other rural land, developed land, and water areas.
The NRI uses this classification
to account for every acre of non-Federal land within
the Nation. Every parcel of land is described by one and only one of these categories.
The NRI approach
to conducting inventories facilitates examining trends
in rural and developed land uses over time because—
- the same sample sites have been studied since 1982;
- the same data have been collected since 1982 [definitions and protocols
have remained the same];
- the inventory accounts for 100 percent of the surface area;
- quality assurance and statistical procedures are designed/developed to
ensure that trend data are scientifically legitimate and unambiguous; and
- it is easy to track lands as they go from one land-use category to another.
Irrespective of the scale of analysis, margins of error must be considered.
Margins of error (at the 95
percent confidence level) are presented for all NRI estimates.
Note that estimates of change between two points in time will be less precise (relatively)
than estimates for a single
inventory year because the changes will be occurring on a smaller fraction of the landscape.
- Land cover/use. A term that includes categories of land cover and
categories of land use. Land cover is the vegetation or other kind of material that covers
the land surface. Land use is the purpose of human activity on the land; it is usually, but
not always, related to land cover. The NRI uses the term land cover/use to identify categories
that account for all the surface area of the United States.
- Forest land. A land cover/use category that is at least 10 percent stocked
by single-stemmed woody species of any size that will be at least 4 meters (13 feet) tall at
maturity. Also included is land bearing evidence of natural regeneration of tree cover (cut
over forest or abandoned farmland) and not currently developed for nonforest use. Ten percent
stocked, when viewed from a vertical direction, equates to an areal canopy cover of leaves and
branches of 25 percent or greater. The minimum area for classification as forest land is 1 acre,
and the area must be at least 100 feet wide.
- Forest land, grazed. A category under forest land cover/use that includes
forest land that is being grazed by livestock and managed using range or pasture management
principles and practices adapted to the forest ecosystem.
- Forest land, not grazed. A land cover/use category that includes areas
meeting the definition of forest land (at least 10 percent stocked by single-stemmed woody species
of any size that will be at least 4 meters [13 feet] tall at maturity) that is not visibly grazed
or otherwise disturbed by domestic livestock.
- Margins of Error. Margins of error are reported for each NRI estimate. The margin
of error is used to construct the 95 percent confidence interval for the estimate. The lower bound of
the interval is obtained by subtracting the margin of error from the estimate; the upper bound is
obtained by adding the margin of error to the estimate. Confidence intervals can be created for various
levels of significance which is a measure of how certain we are that the interval contains the true
value we are estimating. A 95 percent confidence interval means that in repeated samples from the same
population, 95 percent of the time the true underlying population parameter will be contained within the
lower and upper bounds of the interval.
For more definitions see the full
2012 NRI Glossary.
For more information about the NRI, visit
Send comments and questions to the NRI Help Desk
Citation for this website:
U.S. Department of Agriculture. 2015.
2012 National Resources Inventory.
Natural Resources Conservation Service, Washington, DC. 15 January 2016 *
*[use date the website was accessed]