By James Hawks, GIS Specialist, NOAA

In the United States, the National Oceanic and Atmospheric Administration (NOAA) is the authority for nautical charts, marine tides and water levels, shorelines, and positioning. Because there are more and more vessels of all sorts traveling in coastal waters, the comparative safety of ships relative to the seafloor has decreased. This poses significant risk, especially for cargo shipping, since almost 50 percent of all goods shipped are hazardous materials, such as petroleum products. Knowing exactly where a vessel is in relation to the seafloor—even to a matter of inches—improves safety in channels with limited depths, which can vary according to weather and water conditions.

To promote marine safety, including minimizing possible collisions with obstructions, NOAA has maintained a suite of approximately 1,000 paper nautical charts. The maps cover the United States coastline and its territorial waters (including the Great Lakes, Puerto Rico, U.S. Virgin Islands and Pacific islands) and covers an area of approximately 3.4 million nautical square miles. NOAA recently began digitizing these paper charts to create a vector-based database in S-57 format.

S-57 is an International Hydrographic Organization exchange standard for all digital hygrographic information. These digital charts are called NOAA Electronic Navigational Charts (ENCs) and are approved for navigation. They are available free for download at the Office of Coast Survey's Web site (nauticalcharts.noaa.gov).

For this data to be used in GIS systems, however, the data must be translated from S-57 format to GIS format. Therefore, NOAA recently launched ENC Direct to GIS, an ArcIMS site that serves merged ENC data in a variety of GIS/CADD-friendly formats for free download for use in GIS systems. ENC Direct to GIS is located at chartmaker.ncd.noaa.gov/csdl/ctp/encdirect_new.htm.

Nautical Chart Features and Seafloor Mapping

Data sources for NOAA nautical charts include bathymetric data from NOAA hydrographic surveys and topography from aerial surveys, other federal agencies (U.S. Geological Survey, U.S. Army Corps of Engineers, and U.S. Coast Guard), state and local governments, and the private sector. Emphasis is on marine navigation. Approaches to the 40 largest U.S. ports by volume are included. Soundings are shown in meters. Depth curves connect areas of approximate equal depth. The date of sounding data varies considerably from recent multibeam sonar to 19th century lead line surveys depending on area.

In addition to bathymetry, ENC Direct to GIS data includes shipwrecks and obstructions, rocks, bottom characteristics (e.g., mud, sand, coral, and rocks), submarine pipelines and cables, and fish havens. Other data includes U.S. Army Corps of Engineers-maintained channels, aids to navigation (e.g., buoys, lights, day beacons, and landmarks), marine sanctuaries, topography, geographic place names, and various other features. The ENC Direct to GIS site contains more than 200 layers that display this data and its multiple geometry types and is updated monthly so that the latest Electronic Navigational Chart data is available for use in GIS systems for coastal planning, port security, engineering, etc.

Since ArcIMS was already being used throughout NOAA to manage spatial data, it was natural that ENC Direct to GIS was built on ArcIMS, which displays and serves the data stored in the ENC geodatabase and in Esri shapefile format. Each S-57 object class is represented as a layer in the Internet mapping server. The S-57 object classes have been organized into meaningful groups based on category and geometry type in a layer list. ENC Direct to GIS layers can be explored using the Internet mapping server GIS tools. Symbolization of ENC Direct to GIS data is generalized since the data is not for navigation. Geographic place name map labels are produced from object class attribute fields for orientation. Each layer has a scale dependency. This is necessary to keep the service running at a functional level and the map view from being cluttered. Most layers are visible when zoomed in to at least 1:150,000 scale. Smaller scale data is also available via custom requests.

Technical Details

NOAA's ENC Direct to GIS site is hosted on a Windows 2003 server using ArcIMS 9 (HTML viewer) and Apache Tomcat. Data is housed in an Oracle9i database on a Red Hat Linux server with ArcSDE used to spatially enable the data. Data transformations are done via Esri Business Partner Safe Software's Feature Manipulation Engine. Online data transformations are done via Safe Software's Spatial Direct software. Metadata is available for the entire suite, and layer specific metadata is planned for the near future.

Construction of the ENC database is approximately half complete and is scheduled for completion in 2007. ENC Direct to GIS will soon be included in The National Map portal of the United States Geological Survey (nationalmap.gov). Some NOAA bathymetric data is available through its National Geophysical Data Center's Web site (www.ngdc.noaa.gov/mgg/bathymetry/hydro.html). ENC Direct to GIS data is also being used by the U.S. Coast Guard to improve port security.

For more information, contact James Hawks, GIS specialist, NOAA, Office of Coast Survey, Silver Spring, Maryland (e-mail: james.hawks@noaa.gov, tel.: 301-713-2645). Any use of trade, product, or firm names in this article is for descriptive purposes only and does not imply endorsement by the U.S. government.