This datalayer is a polygon coverage representing landcover features located throughout DCW (Digital Chart of the World) geographic coverage as of 1992.
This coverage does not contain an exhaustive inventory of categories. Those included within the Digital Chart of the World were originally intended to assist in navigation. As such, categories such as wetlands, sand, and distorted surfaces are well represented. Additional categories of land cover are present in the VGPOLY (vegetation) coverage, although this coverage is limited to the coterminous United States of America.
Generally, this layer contains two general categories of surface information, Agriculture and Extraction Features and Surface Cover Features such as: cultivated areas, rice fields, cranberry bogs, fish pons, salt pans, lava flows, various types of swamps or wetlands, and more.
This layer was derived from the VMAP0 series produced by the National Geospatial-Intelligence Agency (NGA), formerly known as NIMA (National Imagery and Mapping Agency), an agency of the United States government. VMAP data set products use the "vector product format" (vpf). The term "VMap" is derived from "Vector Smart Map."
Digital Chart of the World is a comprehensive 1:1,000,000 scale vector basemap of the world. It consists of cartographic, attribute, and textual data. The primary source for the database is the National Imagery and Mapping Agency's (NIMA) Operational Navigation Chart (ONC) series. This is the largest scale unclassified map series in existence that provides consistent, continuous global coverage of essential basemap features.
The coverage is is organized into 10 thematic layers which feature a vast number of files organized into libraries. These libraries, or coverages, are geographicially bounded areas, rather than feature-linked coverages.
DCW Layers in the Harvard Geospatial Library are feature-based as we have processed the multiple tiles from the VMAP0 libraries into a series of seamless coverages (e.g. aeronautical features appear in a single layer, "Aeronautical Facilities, Points") which depict a particular feature as it occurs throughout the available geographic coverage areas. Since different geographic areas were mapped by NIMA at different times using various types of feature capture and scanning and digitizing methods and software, multiple map sources of varying dates and multiple processing approaches are represented in each of these HGL layers. We have necessarily generalized the discussion of data source material and process steps in the Data Quality section of this metadata document.