7.2 The GSHHS Shoreline Data Set

The global self-consistent, hierarchical, high-resolution shoreline data base GSHHS is amalgamated from two public domain data bases by Paul Wessel (SOEST, University of Hawaii, Honolulu, HI) and Walter Smith (NOAA Laboratory for Satellite Altimetry, Silver Spring, MD). On the web page of the US National Geophysical Data Center (NGDC)

http://www.ngdc.noaa.gov/mgg/shorelines/shorelines.html

the coastline vector data can be downloaded as MATLAB vector data. First we define the geographic range of interest as decimal degrees with west and south denoted by a negative sign. For example, the East African coast would be displayed on the latitude between 0 and +15 degrees and longitude of +40 to +50 degrees. Subsequently, it is important to choose the coastline data base from which the data is to be extracted. As an example, the World Data Bank II provides maps at the scale 1: 2,000,000. Finally, the compression method is set to None for the ASCII data that have been extracted. The data format is set to be MATLAB and GMT Preview is enabled. The resulting GMT map and a link to the raw text data can be displayed by pressing the Submit Extract button at the end of the web page. By opening the 228 KB large text file on a browser, the data can be saved onto a new file called coastline.txt. The two columns contained in this file represent the longitude/ latitude coordinates of NaN-separated polygons or coastline segments.

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