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Land resource areas used in the United States, Caribbean, and Pacific Basin Major Land Resource Areas (MLRA) Geographic Database serve as the geospatial expression of the map products presented and described in Agriculture Handbook 296 (2022). Land resource categories historically used at state and national levels are land resource units, major land resource areas, and land resource regions (National Soil Survey Handbook, Part 649; Land Resource Hierarchy). Although Agriculture Handbook 296 (AH 296) does not describe land resource units (LRUs) directly, they are the basic units from which major land resource areas are determined. They are also the basic units for state land resource maps. LRUs are commonly but not necessarily coextensive with state general soil map units. LRUs generally are several thousand acres in size. A unit can be one continuous area or several separate areas that are near each other. In 2005, these areas were designated as common resource areas (CRAs) within the Natural Resources Conservation Service (NRCS). Like LRUs, common resource areas are not described in AH 296 and are not shown on the national mapbut are mentioned for historical purposes. Major land resource areas are geographically associated land resource units at a broader scale and higher hierarchical level than LRUs. Land resource regions (LRR) are a group of geographically associated major land resource areasat the highest hierarchical level shown at the continental scale. Identification of these large areas is important in statewide agricultural planning and has value in interstate, regional, and national planning.
In AH 296, major land resource areas are generally designated by numbers and identified by a descriptive geographic name. Examples are MLRA 1 (Northern Pacific Coast Range, Foothills, and Valleys), MLRA 154 (South-Central Florida Ridge), and MLRA 230 (Yukon-Kuskokwim Highlands). Some MLRAs are designated by a letter in addition to a number because a previously established MLRA had been divided into smaller, more homogeneous areas, for example, MLRAs 102A, 102B, and 102C. Other MLRAs, especially smaller ones approaching the LRU scale, have been recombined. The use of numbers and letters to identify the newly created MLRAs requires fewer changes in existing information in records and in databases. A few MLRAs consist of two or more parts separated for short distances by other land resource areas. In some places one of the parts is widely separated from the main body of the MLRA and is in an adjoining LRR. The description of the respective MLRA also applies to these outlying parts. The spatial illustration of the MLRAs has been smoothed for the contiguous United States and Alaska to better reflect the scale at which the MLRA resource attributes (climate, soils, land use, vegetation, geology, and physiography) were aggregated for delineation.