VMap1 Hydrographic Hazards, Points
- This datalayer is a point coverage representing hydrographic hazards or dangers located throughout current VMap1 geographic coverage areas. Features in this layer have a FACC (Feature and Attribute Coding Catalogue) Codes of either BD130, defined as, "Rock; An isolated rocky formation or a single large stone above or below the water surface," or BD180, "Wreck; The ruined remains of a vessel." Additional attributes describe the position of the hazard in relation to mean high tide (e.g. "Above surface/Does not cover at High water" or "Awash at sounding datum" or "Covers and uncovers") This layer was derived from the VMAP1 series produced by the National Geospatial-Intelligence Agency (NGA), an agency of the United States government. VMAP data set products use the "vector product format" (vpf) utilized first by the US Defense Mapping Agency and later by its successor, the National Imagery and Mapping Agency (NIMA, now known as the NGA). "VMap" is derived from "Vector Smart Map." Vector Smart Map (VMAP) Level 1 is a global vector GIS dataset at 1:250,000 scale. This is currently the most detailed global digital dataset freely available and can be downloaded from the National Imagery and Mapping Agency (NGA) website, using the GeoSpatial Engine The coverage is not complete - of the 234 zones which make up the dataset, only around 25% are currently (2002) available - others have not yet been completed or are not declassified. They feature a vast number of files organized into libraries. These libraries, or coverages, are geographicially bounded areas, rather than feature-linked coverages. VMAP Layers in the Harvard Geospatial Library are feature-based as we have processed the multiple tiles from the VMAP libraries into a series of seamless coverages (e.g. Aqueduct Lines appear in a single layer, "Aqueduct Lines") 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.
- VMap 1
- Earth, Northern Hemisphere, Southern Hemisphere, Eastern Hemisphere, Western Hemisphere, Polar regions, Antarctica, Arctic regions, Africa, Asia, Australia, Europe, North America, and South America
- oceans, Transportation, Shipwrecks, Hydrography, and Hydrographic Structures
- Held by:
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