Harmonized World Soil Database (HWSD)

The HWSD is a 30 arc-second raster database with over 16,000 different soil mapping units that combines existing regional and national updates of soil information worldwide (SOTER, ESDB, Soil Map of China, WISE) with the information contained within the 1: 5,000,000 scale FAO-UNESCO Soil Map of the World.  The HWSD represents a major update of the latter map by making much more detailed information available for a significant number of countries.

In addition to the raster database HWSD contains a harmonized soil attribute database in Microsoft Access format. Both can easily be linked in GIS software, allowing the display and query of user-selected soil parameters. The attribute database contains for each HWSD mapping unit information on the soil mapping unit composition, information related to soil phases, and on physical and chemical characteristics of topsoil (0-30 cm) and subsoil (30-100 cm), including organic carbon, pH, water storage capacity, soil depth, cation exchange capacity of the soil and the clay fraction, total exchangeable nutrients, lime and gypsum contents, sodium exchange percentage, salinity, textural class and granulometry. The soil composition is expressed by the attribute table of the HWSD, which provides for each soil mapping unit the component soil types as well as estimated percentages of occurrence. The component soil types are typified by the soil classification units of either the 1974 Legend  of the FAO Soil Map of the World or of the 1990 Revised  Legend of the Soil Map of the World. Globally, for 9,323 mapping units only the 1974 Legend is available, for 26,878 mapping units only the 1990 Legend is available. Therefore the classification into one soil group or another is based on both legends

Users have to keep in mind  that the soil variability shown in the HWSD is often more related to the different scales and levels of detail of the component national maps that contributed to the HWSD than to the real complexity of soil patterns in different areas . Thus the reliability of the information contained in the database is variable: the parts of the database that still make use of the old FAO Soil Map of the World such as North America, Australia, West Africa and South Asia are considered less reliable, while most of the areas covered by SOTER databases are considered to have the highest reliability (Central and Southern Africa, Latin America and the Caribbean, Central and Eastern Europe).