This polygon shapefile represents the shoreline boundary between the Antarctic grounding line and the Antarctic Ocean at low resolution. Low represents an 80 percent reduction in size and quality from the intermediate resolution layer. Grounding lines are the point at which tidewater glaciers start to float in the ocean. The location of the grounding line is important, becasue mass loss from Antarctica is strongly linked to changes in ice shelves and their grounding lines. Changes in grounding lines can result in very rapid changes in glacier and ice shelf behavior. The Global Self-consistent, Hierarchical, High-resolution Geography (GSHHG) Database is a high-resolution geography data set amalgamated from three data bases in the public domain. This layer is part of GSHHG Version 2.3.3. The World Vector Shorelines (WVS) is the basis for shorelines except for Antarctica while the CIA World Data Bank (WDBII) is the basis for lakes, although there are instances where differences in coastline representations necessitated adding WDBII islands to GSHHG. The WDBII source also provides all political borders and rivers. GSHHG data have undergone extensive processing and should be free of internal inconsistencies such as erratic points and crossing segments. Atlas of the Cryosphere (AC) provides the basis for Antarctica coastlines. The shorelines are constructed entirely from hierarchically arranged closed polygons. These shoreline polygon data can be used to simplify data searches and data selections and to study the statistical characteristics of shorelines and land-masses. Wessel, P., and W. H. F. Smith (2014). Shoreline Boundary between Antarctic Grounding Line and the Ocean, 2014 (Low-resolution). (v. 2.3.3). United States. National Geospatial-Intelligence Agency. Available at http://purl.stanford.edu/tg976mv0499. GSHHG used to be called GSHHS (Global Self-consistent, Hierarchical, High-resolution Shorelines) but since rivers and political boundaries were also included we changed it to GSHHG starting with version 2.2.1.
The addition of AC since 2.3.0 allows two choices for Antarctica coastlines: Ice-front or Grounding line. These are encoded as levels 5 and 6, respectively.