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Differences Between ENC and ENC Direct to GIS
NOAA Electronic Navigational Charts (NOAA ENC®) have been developed to support safe navigation in U.S. waters and are available for free download.  NOAA ENCs are in International Hydrographic Organization (IHO) S-57 format, which is the data standard developed by the IHO to be used for the exchange of digital hydrographic data.   NOAA ENCs are fuel for Electronic Chart Display and Information and Systems (ECDIS), which in some cases, may be be used for primary navigation in lieu of paper charts.  In addition, NOAA ENCs may be used to fuel a wide range of less sophositicated Electronic Chart Systems.  

NOAA ENCs can also be used for non-navigational purposes in Geographic Information Systems (GIS).  In order for NOAA ENCs to be used in GIS, the data must be translated from S-57 to a GIS-friendly format. The resulting data can be used for a variety of non-navigational purposes that involve geospatial analyses.

The NOAA ENC Direct to GIS web portal provides comprehensive access to display, query, and download all available NOAA ENC data in a variety of GIS/CAD formats for non-navigational purposes using Internet mapping service technology. Nautical chart features contained within a NOAA ENC provide a detailed representation of the U.S. coastal and marine environment. These data include coastal topography, bathymetry, landmarks, geographic place names, and marine boundaries. Features in a single NOAA ENCs are limited in that they only represent the geographic region that is depicted in that particular NOAA ENC cell. By aggregating nautical features from all NOAA ENCs in the creation of GIS data, a continuous depiction of the U.S coastal and marine environment is achieved.

An ENC contains attributed vector spatial data of nautical chart features. Nautical chart features are organized in S-57 object classes. Attributes in an ENC further describe each nautical feature. Each ENC object class has predefined geometry types associated with it (e.g., point, line, area (polygon in NOAA ENC Direct to GIS)). For example, the land area object class has both point and polygon geometry. An ENC can contain any of the predefined IHO object classes and attributes.

 This is a screen capture of the San Francisco Bay area showing ENC data being displayed through an Electronic Chart System used for navigational purposes.  This is a screen capture of a NOAA ENC that is displayed by Electronic Charting System software. 
 
This is a screen capture from a GIS system showing the same San Francisco bay area in a GIS system.  The system is displaying NOAA ENC data that was downloaded from NOAA ENC®Direct to GIS.    The same NOAA ENC data can be used in a Geographic Information System (in this example, ESRI ArcView).   NOAA ENC data downloaded through NOAA ENC Direct to GIS can be displayed and integrated with other GIS information.  It provides the coastal manager with a powerful tool to display the latest geospatial information found on NOAA charts.   
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