Source / Project IDs refer to the way NGDC organizes the surveys in the GEODAS databases. Marine Trackline Geophysics and Hydrographic Survey 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. The Aeromagnetic Survey database is organized at the first level by Project, a collection of surveys which bear similarities in area, collector or manner of aquisition. A 4 character Project code is assigned. GEODAS uses the Source code as the first 2 characters, or the Project code as the first 4 characters of it's internally assigned NGDC Number, for Marine Trackline / Hydrographic or Aeromagnetic databases, respectively.