Spatial Framework Developed for U.S. Land Resources

Although most Americans consider the United States to be divided into states or regions, one of the highest level ways to divide the country is into natural units called major land resource areas (MLRAs). MLRAs are grouped according to dominant physical characteristics of the land such as land use, elevation and topography, climate, water, soils, and potential natural vegetation. First developed in the 1930s, these distinctions divide the country into certain recognizable regions that are important to policy makers, including U.S. Senate high committees, in determining agricultural and ecological programs.

The Soil Survey Division of the Natural Resources Conservation Service (NRCS), part of the U.S. Department of Agriculture, determines and maintains the MLRAs. Sharon Waltman, soil scientist with the NRCS, simply puts it, "The purpose of our program is to inventory and map the soils of the United States." In 1996, NRCS began to revise the 1984 version of MLRAs using a State Soil Geographic Data Base (STATSGO) polygon delineation at the scale of 1:250,000 instead of the previous versions at 1:7,500,000. The major benefit of this effort is that by using STATSGO and its larger scale, in conjunction with the expert knowledge of NRCS soil scientists, new and more precise national MLRA delineations can be created.

It was soon discovered that with MLRA revisions, the scientists needed to be able to manipulate and map the new data. Waltman proposed using GIS to create a program that would allow the scientists to easily update and revise MLRA data sets without needing to know much GIS technology. This feat was accomplished by Vern Thomas, applications developer, and his Active Response Geographic Information System (AR/GIS) team at the Consortium for International Earth Science Information Network (CIESIN). The MLRA Revision Through Aggregation of STATSGO, or "MARTHA'S," system was built using ArcView GIS software. According to the AR/GIS team, MARTHA'S is "a powerful spatial decision support system for the soil scientist using ArcView GIS and AR/GIS customized functionality. The system expedites refinement of MLRA delineation using STATSGO polygons to generate a new MLRA map data set that contains new, more precise, and accurate delineations that capture soil scientist expertise, knowledge, and spatial reasoning."

The CIESIN team also set up MARTHA'S interface for easy navigation by the soil scientists. The screen is divided into two sides. One side shows a map of the area they are manipulating and the other side contains a legend. This legend is divided into MLRA designated categories such as southern Rocky Mountain foothills and central high plains. There are three important steps that a soil scientist must take in order to make an MLRA revision using the MARTHA'S tool. First, the scientist must determine which of the STATSGO polygons need to be changed to a different MLRA category. They retrieve this information by sifting through the crude data on the database and using their own knowledge. The next step is to decide which MLRA category the set of polygons will change to, according to the legend. Lastly, in order to prevent wrong information from being disseminated and to increase communication between users, the scientist must create a rationale file in the system, which holds information regarding the revision, why it was made, and who made the change.

One of the key uses of the MLRA map coverages, which the MARTHA'S tool has made easier to manage, is the National Resources Inventory (NRI), which is conducted every five years and more recently on a continuous basis. NRCS scientists look at nearly one million points across the nation and determine the conditions of the resources. They look for things like land management, erosion, and cropping systems. MARTHA'S aids in this project by allowing the scientists to update the MLRAs without needing to redigitize new MLRA lines.

The MARTHA'S project also supports an interagency effort to create common ecological regions (www.essc.psu.edu/soil_info/soil_lrr). In conjunction with other environmental agencies such as U.S. Forest Service, U.S. Environmental Protection Agency, the National Park Service, and others, the NRCS is working toward a cooperative effort that will lead to further research of the land and enhanced communication between the different government agencies. Many of these departments have been conducting independent studies of the similar regions, and by bringing them together under this program there will be increased sharing of knowledge, experience, and technology.

The GIS-based MARTHA'S tool is creating a common and efficient mode of communication and revision for the NRCS. With its aid, soil scientists and other scientists can spend less time on tedious revision work and more time on important research that will benefit the community. Since their work directly affects the decisions that are made on behalf of our land resources, it is important that the most advanced GIS technology be at their disposal.

For more information, contact Sharon Waltman, soil scientist, soil taxonomy and standards staff, USDA–NRCS (e-mail: sharon.waltman@nssc.nrcs.usda.gov, tel.: 402-437-4007).

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