This map shows the distribution of the principal kinds of soil in the USA as classified in the system currently used by the soil survey. The map can be used only for comparing soils of large areas. It has 331 units defined mostly as associations of phases of great groups. A brief legend on the front of the map explains the colors that distinguish soil orders, lists the symbols for dominant great groups and special features, and includes an introduction to the nomenclature. A detailed legend on the back of the map is arranged alphabetically by great groups within a suborder of each order. The legend provides general definitions for the orders, suborders, and great groups, present dominant land use for the suborders, and approximate equivalent former names for the great groups. The map, scale 1:7,500,000, size 48 by 71 cm, was compiled on the National Atlas base with an Albers equal area projection. The soil information is current as of December 1967. The base map shows state boundaries, major drainages, principal cities, and state experiment stations. The soil map, in color, is for sale by the U. S. Geological Survey, 1200 S. Eads Street, Arlington, Va. 22202.

The Seventh Approximation sharpens the relationship between soil classification and soil geography; and it is likely to lead to more valid geographic correlations between genetic factors and soil morphology. Although the Seventh Approximation is expected to bring about only a few changes on large-scale, detailed soil maps, the opposite is true for small-scale, general soil maps. Even on the general maps, however, many, perhaps most, soil boundaries will appear where they would have appeared using the current soil classification; but the changes will be drastic in the nomenclature. The fact that substantive names are, or will be, provided for all classes in all categories makes soil classes of all categories available for use on maps. This fact makes possible a better matching of categorical and cartographic levels of generalization. The Seventh Approximation does not alter the need for the concepts of soil phases and soil associations.

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Compilation of a new general soil map of the USA is under way. A new map is needed to provide new information accumulated over the past 20 or 30 years, to express our knowledge about soils in terms of the new classification, and to incorporate new ideas in map and legend design that improve interpretation potential. An experimental map, on which most map units are geographic associations of great groups of the new classification, is being compiled on a 1:7,500,000 base. In the legend, map units are grouped under the order, suborder, and great group of their most extensive soils, an organization which permits three levels of generalization. The map will be published in the National Atlas of the USA being prepared by the US Geological Survey.