To determine how well the biological diversity of a region is protected, one must know the locations of all managed areas and the level of management being provided at each. In this paper we outline some of the problems confronting cartographers in compiling digital maps of managed areas. These problems involve the classification of management levels, selection of a minimum mapping unit, integration of maps from multiple sources, and the maintenance of data on rapidly changing land ownership. We demonstrate how these problems were resolved for a managed areas map for the state of California. Characteristics of an ideal geographic information system (GIS) database of managed areas are also described. The California map is being produced at a scale of 1:100,000 with a minimum mapping unit of 200 ha for uplands and 80 ha for wetlands. Mapping has been completed for the Southwestern California Ecoregion, and the results and lessons learned are reported here. For this 3-million-ha study region, 9.8% of the total land area was classified at the highest level of protection; these managed areas are concentrated in higher elevation areas. Only 12.1% of significant natural areas in the region, as identified by the California Lands and Natural Areas Program, are currently within well-protected areas.