DCW Political and Oceans Features, Polygons
- This datalayer is a polyfon coverage representing political and ocean feature areas found throughout DCW (Digital Chart of the World) geographic coverage as of 1992. Ocean features shon here include areas of pack ice, shelf ice and open ocean. The Political/Oceans layers provide a common visual definition of countries rather than a legal one. The legal definition of a coastal country would include offshore ocean areas, while with a graphic depiction, the country ends at the ocean shoreline. Please note that the ocean shoreline is included in the Political/Oceans line coverage only and is not repeated in the Drainage or Hypsography layers. This type of feature organization enables selection of countries as areas and the distinction of the land and water areas of the world. 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.
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