J. Final Outer Limits

Owned by Harald Sund (Unlicensed)
Last updated: Oct 16, 2015 by Tore Sannes (Unlicensed)
7 min read

Introduction

UNCLOS Article 76 states that "The coastal State shall delineate the outer limits of its continental shelf, where that shelf extends beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured, by straight lines not exceeding 60 nautical miles in length, connecting fixed points, defined by coordinates of latitude and longitude."

At this point we have created all the formula lines and constraint lines and we can proceed to construct the final outer limit. The construction of outer limits is a complex operation but the Generate Outer Limit tool is designed to assist you in the best possible way. The tool lets you digitize and combine line segments and keep distances between points less than 60M. Sometimes it is best to do this area by area and in multiple steps, then combining points into one or more final outer limits. In many cases the best approach is to construct and outer edge line consisting of only Hedberg points, Gardiner points and the 200M line, and then construct a constraint line consisting of the 350M line and the 2500m + 100M isobath. These two lines can then be combined into one final outer limit.

In the exercises in this section we will try to produce a final outer limit using the Generate Outer Limit tool.

Exercises

The Outer Limit Menu

Before we can use the Generate Outer Limit tool we need to populate the 4. Outer limit folder with the necessary data. If you look at the folders inside the outer limit folder you will see three folders called; Constraints, Formulae and Outer Limit. We need to copy our distance lines, Hedberg points and Gardiner points into these folders.

Exercise

Copy your data to the Outer limit folder

  1. In the folder 1. Martime lines / 200M lines right click Baseline_Atlantis + 200M and click Copy.
  2. In the folder 4. Outer limit right click the folder Formulae and click Paste.
  3. In the folder 1. Martime lines / 60M lines select all the lines, right click, and click Copy.
  4. In the folder 4. Outer limit right click the folder Formulae and click Paste.
  5. In the folder 3. Sediment Data / Sediment Thickness Points select all the lines, right click, and click Copy.
  6. In the folder 4. Outer limit right click the folder Formulae and click Paste.
  7. In the folder 1. Martime lines / 100M lines right click atlantis's 2500 meter isobath + 100M and click Copy.
  8. In the folder 4. Outer limit right click the folder Constraints and click Paste.
  9. In the folder 1. Martime lines / 350M lines right click Baseline_Atlantis + 350M and click Copy.
  10. In the folder 4. Outer limit right click the folder Constraints and click Paste.

All necessary data should now be in one of the folders in the Outer limit folder.


 When digitizing the outer limit it is possible to activate different datsets to be available during the construction of the outer limit. We can now take a closer look at the Outer Limit Menu.

Exercise

Getting familiar with the Outer Limit Menu

  1. Right click the folder 4. Outer limit and click Generate Outer Limit
  2. Observe the different datasets and folders in the menu.
  3. Check the box next to the Formulae folder.
  4. Click the display icon at the top of the menu to display all the activated datasets.


The Outer Limit Menu

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Digitize the Outer Limit

We can now start to digitize the outer limit. We will do this in three steps; first digitize the outer edge consisting of formula lines, then digitize a constraint line consisting of the distance constraints, and then finally combine these two lines.

The digitizer has a range of different keyboard shortcuts that you need to use when constructing an outer limit:

  • left click (mouse) - will snap to the closest point on any line.
  • c - crossing lines - will insert a new point between two lines, or a line and the 60NM circle. 

  • d - delete - will delete the last digitized point.

  • l - connect to line - will insert a new point on the line at the cursor position.

  • s - select line piece - will select all the points on a line until next crossing line or to end of line. 

  • m - multiple selection - will select all points from previous point to picked point (mouse cursor location).

 

For the first exercise we have included a screen shot of the steps in the exercise.

Exercise

Digitize the outer edge

  1. Click the Start Digitize button.
  2. Snap to a point on the 200M line by placing your mouse cursor over the line in the East Sea area and clicking the left mouse button.
  3. We are now going to follow this line north until we meet the crossing 60M line. Place your cursor close to the crossing between the 200M line and the 60M line and press s on the keyboard.
  4. We now want to follow this 60M line until me meet the next crossing 60M line. Place your cursor close to the crossing between the 60M line we are at and the next 60M line and press s.
  5. Again we want to follow this 60M line until me meet the next crossing 60M line, but we want to make sure it follows the outer part of the 60M line. Place your cursor somewhere on the outer part of the 60M line and press m.
  6. Follow the line to the next 60M crossing line by placing your cursor close to the crossing between the 60M line we are at and the next 60M line and press s.
  7. We now want to follow this 60M line until me meet the crossing 200M line. Place your cursor close to the crossing between the 60M line we are at and the 200M line and press s.
  8. We now want to follow the 200M line until me meet the crossing 60M line again. Place your cursor close to the crossing between the 200M line and the crossing 60M line and press s.
  9. We now want to follow this 60M line until we can reach the sediment thickness points. Place your cursor further up on the 60M line and press m.
  10. When you can see the sediment thickness points inside the white circle you can connect to them by clicking the left mouse button. Tip: place the cursor outside the point furthest out to snap to the "maximum" point.
  11. Continue to click the left mouse button until you have passed the sediment thickness area.
  12. We now want to connect to the 60M line in the north. Place your cursor close to the crossing between the 60M line and the white 60M circle and press c.
  13. We now want to follow this 60M line until me meet the crossing 200M line, but we want to make sure it follows the outer part of the 60M line. Place your cursor somewhere on the outer part of the 60M line and press m.
  14. Follow the line to the 200M crossing line by placing your cursor close to the crossing between the 60M line and the 200M line and press s.
  15. We now want to follow this 200M line a little bit further to the west. Place your cursor somewhere to the west on the 200M line and press m.
  16. Stop digitizing by clicking End Digitize.
  17. You will be asked to specify a name. Type in Outer Edge Limit and click OK.
  18. The dataset is stored in 4. Outer limit / Outer Limit click OK.
  19. Click Close to close the Outer Limit Menu.

 

The digitized outer limit lines contains a lot of important metadata which will be used in the documentation. Each point on the outer limit line will refer back to the original FOS point or basepoint. It also contains information on point distance, shot point, sediment thickness and a lot more.

Exercise

Investigate the Outer Edge Limit line metadata

  1. In the folder 4. Outer limit / Outer limit right click Outer Edge Limit and click Table View.
  2. Look at the information in the different columns and scroll down the list of points.
  3. Click Close when you are done.

 

One important part of the outer limit line definition is that it should consist of: straight lines not exceeding 60 nautical miles in length, connecting fixed points. This means we can bridge some of the concave areas of the Outer Edge Line to gain more area

Exercise

Optimize the Outer Edge Limit

  1. In the folder 4. Outer limit / Outer limit right click Outer Edge Limit and click Optimize outer limit.
  2. Keep the default settings and click Execute. The result will be stored in the same folder.
  3. Click OK to close the menu.
  4. In the folder 4. Outer limit / Outer limit right click Outer Edge Limit Optimized and click Display.
  5. Investigate the areas that have been bridged.

 

 

The Optimize outer limit tool is based on angle calculation and not area calculation. The angles are calculated in what ever coordinate system the data is in. Thus, It cannot be assumed this tools will automatically produce the absolute maximum achievable area.

 

We are now going to digitize the constraint line. It is important to remember that we want to select the constraint line which is furthest out at any point. 

Exercise

Digitize the constraint line

  1. Make sure the graphics window has been cleared by clicking X.
  2. Right click the folder 4. Outer limit and click Generate Outer Limit.
  3. Check the box next to the Constraints folder.
  4. Click the display icon at the top of the menu to display all the activated datasets.
  5. Click the Start Digitize button.
  6. Digitze the constraint line using a combination of your mouse and keyboard short cuts.
  7. Click End Digitze.
  8. You will be asked to specify a name. Type in Constraint Line and click OK.
  9. The dataset is stored in 4. Outer limit / Outer Limit click OK.
  10. Click Close to close the Outer Limit Menu.

 

Finally we can produce the final outer limit. Follow the Outer Edge Optimized where it is inside the Constraint Line, else follow the Constraint Line. In the 1% sediment area, connect by the 60M Circle.

Exercise

Produce Final Outer Limit

  1. Make sure the graphics window has been cleared by clicking X.
  2. Right click the folder 4. Outer limit and click Generate Outer Limit.
  3. Check the box next to the two datasets Outer Edge Limit Optimized and Constraint Line.
  4. Click the display icon at the top of the menu to display all the activated datasets.
  5. Click the Start Digitize button.
  6. Digitze the final outer limit line using a combination of your mouse and keyboard short cuts.
  7. Click End Digitze.
  8. Keep the default name and click OK.
  9. The dataset is stored in 4. Outer limit / Outer Limit click OK.
  10. Click Close to close the Outer Limit Menu.

 

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