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FAQs: ENC Direct to GIS

Frequently Asked Questions

Visit How-To for more explicit directions on various features.

Click on a question to jump to the answer.

  1. Which Web browsers work with ENC Direct to GIS?
  2. Can I use ENC Direct to GIS for navigation?
  3. How does data from ENC Direct to GIS differ from data found in the respective NOAA ENC?
  4. What is the source of information for data used in ENC Direct to GIS?
  5. Where do all of the data layers originate?
  6. Where can I find information about the ENC Direct to GIS layers?
  7. How are the data layers organized?
  8. What is the coordinate system for data used in ENC Direct to GIS?
  9. Why are some of the S-57 object classes separated into individual geometry layers (point, line, polygon)?
  10. Why can I only see certain layers when I am zoomed into a particular scale?
  11. What is the update frequency of ENC Direct to GIS and how accurate is the data?
  12. How do I download ENC data from ENC Direct to GIS?
  13. How long will it take to download my data?
  14. What is the map projection for ENC data displayed?
  15. When extracting data, how many scale bands do you recommend per extraction?
  16. When drawing multiple areas for extraction, does it extract from all or just the last box drawn?

Answers

Question 1 - Which Web browsers work with ENC Direct to GIS?

Answer - ENC Direct to GIS has been tested to work with Internet Explorer Version 7 and later, Firefox Version 17 and later, Google Chrome Version 23 and later, and Safari Version 5 and later.  (Back to top)

Question 2 - Can I use ENC Direct to GIS for navigation?

Answer - No, ENC Direct to GIS is not certified for navigation. You can download NOAA ENCs for navigation.   (Back to top)

Question 3 - How does data from ENC Direct to GIS differ from data found in the respective NOAA ENC?

Answer - ENC Direct to GIS data is in a format not certified for navigation. The data is derived from the official NOAA ENCs through GIS conversion software.  (Back to top)

Question 4 - What is the source of information for data used in ENC Direct to GIS?

Answer -
The source for the ENC data is the published ENC cells.  The source for each base map used in ENC Direct to GIS is:

  • World: This is a National Geographic World Map rest service developed by National Geographic and ESRI, available from ESRI’s ArcGIS Online website.
  • Street: This is a World Street Basemap rest service provided by ESRI, available from ESRI’s ArcGIS Online website.
  • Aerial: This is a World Imagery rest service provided by ESRI, available from ESRI’s ArcGIS Online website.
  • Topo: This is a World Topographic Map rest service provided by ESRI, available from ESRI’s ArcGIS Online website.
  • Ocean: This is a World Ocean Bathymetric Map rest service provided by ESRI, available from ESRI’s ArcGIS Online website.
  • Raster: Raster image service produced and maintained by NOAA.  (Back to top)

Question 5 - Where do all of the data layers originate?

Answer - The data layers have been created by merging S-57 object classes from all NOAA ENCs into seamless layers. For example, the coastline layer for the Harbour scale band is a composite of the S-57 object class COALNE from all current Harbour ENCs.  (Back to top)

Question 6 - Where can I find information about the ENC Direct to GIS layers?

Answer - Use the free S-57 object catalog to look up layer and attribute definitions. (This service is for informational purposes only and does not constitute an endorsement by the U.S. Government.) In addition, you may click the 'Description' from the 'ENC Scale Band' drop down list for each scale band to get a list of available GIS layers. (Back to top)

Question 7 - How are the data layers organized?

Answer - The data layers are grouped in folders by thematic categories that describe the layers that they contain. ENC Direct to GIS contains more than 200 data layers, which are found by navigating through the appropriate folders/subfolders.  (Back to top)

Question 8 - What is the coordinate system for data used in ENC Direct to GIS?

Answer - Data used is in GCS-WGS 1984 coordinate system.  (Back to top)

Question 9 - Why are some of the S-57 object classes separated into individual geometry layers (point, line, polygon)?

Answer - S-57 object classes contain multiple geometry types. For example, the WRECKS object class can contain point and polygon features. It is important to note that an S-57 object in ENC Direct to GIS can have point, line, and polygon parts.  (Back to top)

Question 10 - Why can I only see certain layers when I am zoomed into a particular scale?

Answer -
Layers are configured with scale dependency. The data is displayed by scale band. As you zoom in at certain scale ratio, the application will display ENC data compiled for that scale band. For example, if you zoom in at scale 1:36,112, the application will display ENC data within the Approach and Harbour scale band. If you would like to find out which scale band you are viewing, simply click on the screen and a popup window will appear displaying the current ENC name.  

In addition, in order to speed up the map service and reduce data clutter in the map frame, the point layers for the Overview scale band are displayed at a smaller scale within the Overview scale range. The scale range for the Overview scale band is ranged 1:1,500,001 or smaller. The line and area features are visible with a minimum scale ratio of 1:4,622,324. The point layers are visible with a minimum scale ratio of 1:2,311,162.  (Back to top)

Question 11 - What is the update frequency of ENC Direct to GIS and how accurate is the data?

Answer - The NOAA ENC cells intended for navigation are updated for Notices to Mariners and other safety information. These updates are provided to navigational users of NOAA ENC cells as update patches. Periodically, NOAA ENC cells are released as complete new versions (called New Editions when referring to paper charts) that include all of the update patches.

ENC Direct to GIS data is updated every Saturday night. This includes all of the update patches or new editions available at that time.

Data contained in ENC Direct to GIS retains the accuracy of the original NOAA ENC data.  (Back to top)

Question 12 - How do I download ENC data from ENC Direct to GIS?

Answer -

  • Click the “Data Extract” button from the top toolbar and choose one of the scale bands from which to download data. For example, selecting ‘Extract Overview’ allows you to download data within the Overview scale band.
  • Select the desired draw tool in 'Select area' and draw the shape on the screen to identify the chosen geographic area.
  • Check the box(es) next to the layer name(s) to select layer(s) to download.
  • Select the file format for the output.
  • Click ‘Extract.’
  • You will be prompted to save a .zip file locally. Please note: Each data extract will be saved with the same .zip filename. Be sure to rename your downloaded file before the next download in order not to overwrite your previous data.
You can download data without having the data visible on the screen.  (Back to top)

Question 13 - How long will it take to download my data?

Answer - The time varies and depends on your Internet connection and the amount of data you wish to download. Downloading layers that have a smaller spatial extent is generally quicker than downloading layers for a large spatial extent.  (Back to top)

Question 14 - What is the map projection for ENC data?

Answer - The majority of NOAA charts use a Mercator projection, classified as a cylindrical projection upon a plane, the cylinder tangent along the equator. The Mercator is the most common projection used in maritime navigation, primarily because rhumb lines plot as straight lines.

All ArcGIS services and basemaps are stored with a continuous tiling system to support the seamless display of map data for large scale subareas. This requires a single map projection for the world. The spherical Mercator projection is used. This is often referred to as the WGS 1984 Web Mercator [Auxiliary Sphere] projection.  (Back to top)

Question 15 - When extracting data, how many scale bands do you recommend?

Answer - We recommend selecting one scale band per extraction. If you select more than one scale band during the extraction process, you will obtain duplicate data at different resolutions. We recommend selecting the best scale band for the type of application for which you require the data.  (Back to top)

Question 16 - When drawing multiple areas for extraction, does it extract from all or just the last box drawn?

Answer - The extraction tool gives you the ability to select more than one area. You will need to select the area polygon box again to draw more than one selected area. The extraction file will not separate the object classes by the different selected areas.  (Back to top)

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