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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

Get 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 icon at the top of the menu to display all the activated datasets.


The Outer Limit Menu

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)

 

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 are 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
Exercise

Generate the Outer Limit

In this exercise we are going to digitize the outer limit from your formula, and constraint lines using the Outer Limit menu.

  1. Copy all your formula lines to the 4. Outer limit / Formulae folder (200M, FOS+60, Sed>1% points)
  2. Copy all your constraint lines to the 4. Outer limit / Constraints folder (350M, 2500m + 100M)
  3. Open the Outer limit menu, and check some of the datasets and use the Display and scale buttons


The Outer Limit menu with Datasets Copied

Exercise Continued
  1. Digitize a combined formula line, by clicking the digitize button and following the instructions
  2. When you have finished digitizing and clicked the end digitize button, give the new dataset a name, such as combined formula line.
  3. Right click the new line in the project, and select Table view
  4. Observe the new columns in the table

 

There are also two tools which have been developed in order to Optimize the outer limit and to Maximize the outer limit. These tools should be used with great care in order for them to be utilized correctly. It cannot be assumed these tools will automatically produce the absolute maximum achievable area. They are interactive tools that should be experimented with, using different settings until the desired result is obtained.



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