Source 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, meaning the institution, agency or other organization which collected the data, or in some cases the contributor of the data. A 2 character Source code is assigned by NGDC. GEODAS uses this Source code as the first 2 characters of it's internally assigned NGDC Number.