Skip past header information
USGS - science for a changing world

Open-File Report 2014-1040


Polygons of Global Undersea Features for Geographic Searches


Data Sources

Skip past contents information

Many of the undersea features in the shapefile were selected from a list assembled by Weatherall and Cramer (2008) in a report from the British Oceanographic Data Centre (BODC) to the GEBCO Sub-Committee on Undersea Feature Names (SCUFN). Annex II of the Weatherall and Cramer report (p. 20–22) lists 183 undersea features that "may need additional points to define their shape" and includes online links to additional BODC documents providing coordinate pairs sufficient to define detailed linestrings for these features.

For the first phase of the USGS project we created polygons for 87 of the undersea features on the BODC list, using the linestrings as guides; the selected features were primarily ridges, rises, trenches, fracture zones, basins, and seamount chains. Polygons for an additional 224 undersea features, mostly basins, abyssal plains, and fracture zones, were created in the second phase of the USGS project. Polygons were created and compiled in a single shapefile, using ArcGIS® version 9.3.1, with the aid of historical bathymetric maps and bathymetric raster data—the ETOPO1 global relief model (National Geophysical Data Center, 2009) was used unless noted otherwise in the COMMENTS attribute field. Primary scientific literature was used to resolve ambiguous feature extents and is cited in the COMMENTS attribute field. Adjacent polygons were snapped together, except for clearly overlapping and nested features.

The UFI and DSG attributes follow the GEOnet Names Server geographic information system (GIS) compatible format (http://geonames.nga.mil/gns/html/gis_countryfiles.html). UFI and DSG values are taken from the GNS database. The federally approved name in GNS is given in the UF_NAME attribute field (except as noted in the COMMENTS attribute field). Variant names used by GEBCO or in some USGS publications are listed in the VAR_NAME attribute field if applicable. Polygon centroids (CENT_LAT and CENT_LONG attribute fields) were determined using ArcGIS® Calculate Geometry, in the WGS 84 geographical coordinate system. (CENT_LONG values for features crossing the 180th meridian were estimated by inspection in ArcMapTM.) The centroid of a highly irregular or nonconvex feature may fall outside the perimeter of the polygon, as this calculated value represents the average center.

Depth ranges included in the COMMENTS attribute field for some features represent the approximate depth in meters below sea level. These values were obtained by examining bathymetric maps and bathymetric raster data to determine the minimum and maximum depths that define the feature and its spatial extent. Depth ranges typically apply to features such as basins, plains, and seamounts, which are reasonably defined by closed isobaths, but do not apply to features such as canyons, fans, and escarpments. AREA_SQKM values were determined using ArcGIS® Calculate Geometry, with datum WGS 84 and sinusoidal (equal area) projection. The sinusoidal projection preserves area but distorts perimeter values for high-latitude features.

To create the linked data, the vertices of the polygons were extracted from the shapefile in ArcMapTM along with the values of five selected attributes: UFI, DSG, UF_NAME, VAR_NAME, and COMMENTS. The coordinate pairs (vertices) were converted to WKT notation for polygons and three new attributes were added to the five extracted from the shapefile: GNS feature notes (from GNS advanced search), use constraints (condensed from the shapefile metadata), and a link to the source shapefile (as compressed in undersea_features.zip). The WKT and attribute values for each feature were assembled in a spreadsheet and then converted to linked data in Turtle format (Terse RDF Triple Language) following the recommendations of the World Wide Web Consortium (W3C, 2014, 2015) and Open Geospatial Consortium (OGC, 2012). This conversion required relabeling and merging some of the attributes to fit the classes and properties typically employed in linked data. In addition, the undersea feature designations, codes, and definitions employed in GNS (see United States Board on Geographic Names, 2005) were also converted to linked data.

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubsdata.usgs.gov/pubs/of/2014/1040/ofr2014-1040-data_sources.html
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Monday, 25-Jun-2018 10:04:38 EDT