Platform IDs refer to the way NGDC organizes the surveys in GEODAS Marine Trackline Geophysics and Hydrographic Survey databases. These databases are organized at the first level by source organization, and at the second level by Platform, meaning the research vessel which collected the survey data. (or occationally another grouping of surveys, such as country). A 4 character Source code is assigned by NGDC, the first 2 of these being the Source Identifier, so the 4 character id identifies a specific platform operated by a specific organization. GEODAS uses this Source/Platform code as the first 4 characters of it's internally assigned NGDC Number.