NOAA ENC®		DNC®

DEFINITIONS
The NOAA ENC® is based on the International Hydrographic Organization Transfer Standard for Digital Hydrographic Data, Publication S-57 and is approved by the International Maritime Organization for SOLAS class vessels to use for navigation in an Electronic Chart Display and Information System (ECDIS).   NOAA and the U.S. Army Corps of Engineers (USACE) are producing ENCs for the coastal and inland waters of the U.S.   Most hydrographic offices throughout the world are producing vector charts in ENC format.

The Digital Nautical Chart® (DNC®) is produced by the National Geospatial-Intelligence Agency (NGA) and is an unclassified, vector-based, digital database containing maritime significant features essential for safe marine navigation.   The DNC® uses the Vector Product Format, which is a NATO standard for digital military map and chart data.   NGA produces DNC®s for worldwide coverage.

Both NOAA ENC® and DNC® (in U.S. waters) are based on NOAA nautical charts, just in different formats.  The NOAA ENC®, however, has certain critical features such as aids to navigation and channel limits created from larger scale, more accurate information than can be obtained by digitizing a paper or raster nautical chart. To the indiscriminant electronic chart user, NOAA ENC® and DNC® functionality appears to be identical.   With appropriate software, both can provide safety and danger warnings.

SOME IMPORTANT DIFFERENCES
While both ENC and DNC® are vector, they have different spatial data models.   An ENC has two layers (skin of the earth and everything else), while a DNC® has 12 layers of information.   An ECDIS must transform the ENC into a "System" ENC for use.   This essentially means full topology must be constructed from the less complete Chain-node topology of the ENC. A DNC® is topologically complete, i.e. all 12 layers of information are fully attributed, and can be "directly read" by ECDIS-N.

ENC was developed for civil navigation, with an initial emphasis on commercial navigation.   DNC® was developed for the military user for multiple roles; it can be combined with land, air and tactical data layers for various military uses such as littoral warfare.

During the creation of a NOAA ENC®, high-resolution source information was used in portraying channels, aids to navigation, and other important features.  Today, NOAA ENC® data is updated by incorporating high resolution source information from a variety of sources.  DNC®s covering U.S. waters were created by digitizing paper NOAA charts.

The NOAA ENC® files are updated using weekly USCG Local Notice to Mariners and NGA Notice to Mariners. DNC®s are updated on a monthly basis using NGA Notice to Mariners.  For US Waters, NGA updates the data inside the 12' contour by using USCG local notices. We started this practice about four years ago at the request of the USCG.

LINKS
NOAA ENC®
NGA's DNC® Home Page
USACE Inland ENCs (IENCs)