Electronic Navigational Chart (ENC) cells are available as Base Cells or Update Cells.
	Each ENC has an Update Application Date and Issue Date.
Base Cells are made available when each New Edition of an ENC is produced.
-	The Update Application Date is the date that a Base Cell becomes available.
-	In general, a Base Cell is produced when significant changes have been made to the ENC's coverage area, such as application of a hydrographic survey, channel alignment or shoreline modification.
-	A new edition may also be issued if a large number of Update Cells have been released for the same edition.
-	A Base Cell contains all the cartographic data within the coverage area of the ENC.
-	The filename extension for a Base Cell is 000.
Update Cells can be made available many times during the edition life of an ENC.
-	The Issue Date is the date that an Update Cell becomes available.
-	In general, an Update Cell is produced when a critical change has been made to the ENC, such as a Notice to Mariner correction.
-	An Update Cell only contains the cartographic data associated with the critical change and it must be applied to the Base Cell.
-	The filename extension for an Update Cell is the number of the update, such as 001, 002, etc. These numbers are sequential and without omission.