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Illinois Cooperative Soil Survey The Next Generation and MLRA Concept


Illinois Cooperative Soil Survey

The Next Generation and MLRA Concept

"I hope the answer to your question is clearly indicated in what I have written. It is that the soil survey will never be completed because I cannot conceive of the time when knowledge of soils will be complete. Our expectation is that our successors will build on what has been done, as we are building on the work of our predecessors." R. S. Smith, Director, Illinois Soil Survey in September 27, 1928.

The above quote is from a letter by R. S. Smith in response to the Comptroller of the University of Illinois' request for an estimate of the cost to complete the soil survey of the state. That was more than 80 years ago! A response today would be quite similar!


The initial soil mapping of Illinois was completed in 1995. The data was gathered over a period of about 45 years, on a county by county basis, and reflected what was known about the soils at the time of the survey. Each survey area, as surveyed, was state-of-the-art at that time. However, there was a need to bring the patchwork of county soil surveys to a common standard, to build on the existing information, and to develop a coordinated database to address state, regional, and national concerns. The published soil survey reports were excellent sources of information, but there was a recognized need to keep up with an increasing demand for soil survey information. As demographics, technologies, environmental concerns, and intensities of land use changed the soils information had to change as well to maintain the state-of-the-art status.


In 1992, an approach for updating and maintaining "modern" soil surveys was initiated. The existing soil surveys were a good product to start with, so the job of updating soil surveys was not to produce an entirely new survey, but to, where possible, upgrade the existing survey be refining and enhancing it. The update of an existing soil survey would depend on the accuracy, precision, and usefulness of the original survey. New techniques had been developed and improvements had been made in the use, interpretations, and presentation of soil survey information. As new information about soils was gathered the soil surveys were to be updated to meet the broad-based demand for, and use of, soil survey information throughout Illinois. That demand was increasing and users wanted resource information data layers like the soil survey, incorporated into geographic information systems (GIS). There was a need to correlate soils information based on a geographic basis rather than by political boundaries. Thus, it was determined that all update activities would be managed by Major Land Resource Area (MLRA).

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In the 1960's USDA divided the United States into land resource regions (LRR) and major land resource areas (MLRA). This system affords a basis for making decisions about national and regional agricultural concerns, provides a broad base for extrapolating the results of research and resource inventories within national boundaries, and serves as a framework for organizing and operating resource conservation programs. The 24 land resource regions of the USA have been divided into 212 MLRA's. MLRA's are geographically associated areas that are characterized by a particular pattern of soils, climate, water resources, and land uses. Parts of 15 MLRA's in 6 LRR's cover Illinois. MLRAs of Illinois Some of the MLRA's have been subdivided into land resource units or common resource areas. Illinois Common Resource Areas

The soil survey area of today is the MLRA, not an individual county, as in the past. Location map of MLRA Offices Soil survey identification legends, taxonomic and map unit descriptions and correlation activity is on an MLRA basis. Soil maps will join across political boundaries (county and state) line for line, map symbol for map symbol, map unit name for map unit name, and soil interpretation for soil interpretation. The objective of all MLRA soil survey update activities will be to provide an improved product on a controlled base, that can be used in a geographic information system (GIS). Significant improvements expected include:

  • A uniform map scale and mapping intensity for the MLRA

  • A common standard of documentation.

  • Better description of composition and pattern of soils in map units.

  • More precise statements about the expected reliability of maps and interpretations.

  • New soil property data and interpretations.

  • A coordinated database of soil properties.

  • A digital soils data layer meeting national map accuracy standards.


The following guidelines are used to produce a 1:12,000 (12K) digital soil survey for Illinois:

  • Survey Area is the MLRA with county projects as possible subsets.

  • Base will be USGS digital orthophoto quarter quads (DOQ).

  • Scale of the DOQ's is 1:12,000.

  • Legend will be an MLRA legend with a typical pedon described for each taxonomic unit and map unit in the MLRA.

  • Documentation is required in order to make unbiased, statistically reliable statements of map unit composition. This will require transects and descriptions throughout the MLRA in addition to any fieldwork that may be needed in county subsets.

  • Product will be a coordinated, joined, digitized soil survey on a 1:12,000 orthophoto quarter quad base.


Since 1992, soil survey update projects (the "next generation") have been completed in 75 counties through cost share agreements. Digital soils data is available for all 102 counties in Illinois on the Web Soil Survey and Soil Data Mart. Soil survey users need more, want more, and expect more from the soil survey. The soil survey partnership is dedicated to delivering a quality product.