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.
Exercises
The Outer Limit Menu
The "Outer Limit Menu" is used in order to select the final outer limit points from the formula and constraint lines. This command is available from the folder 4. Outer limit.
The Outer Limit Menu
The folders in the Outer Limit menu correspond to the sub folders in 4. Outer limit. You will also be able to see the datasets in this list. Before opening this menu, you can copy the files you want to use in your outer limit to the correct folders.
You can display the different data sets by checking the data sets you want to display, and clicking the pencil. Multiple select is allowed in this list. You can scale the display window to the data sets the same way by checking the datasets, and clicking the scale button.
The digitize button is used to digitize points from the checked data-sets. You can use this to pick points on your final outer limit. Each time you pick a point, a white circle of 60M will be displayed around the last picked point. The circle is geodetic correct. This will be a guide to you when digitizing the final outer limit. The distance between the final outer limit points should be less than 60M, so the next point you pick should be inside the circle.
Try the Outer Limit tool
Before doing the exercise below, get a hand on feeling with the functionality of the digitizer, just by playing around with two datasets.
- Copy the 200M line into 4. Outer limit / Formulae
- Copy your 2500m + 100M into 4. Outer limit / Constraints
- Display the data from the Final Outer Limits panel. Note that the data may also be displayed from the project, e.g. Display Points.
- Try the various digitizing operations.
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.
- Copy all your formula lines to the 4. Outer limit / Formulae folder (200M, FOS+60, Sed>1% points)
- Copy all your constraint lines to the 4. Outer limit / Constraints folder (350M, 2500m + 100M)
- 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
- Digitize a combined formula line, by clicking the digitize button and following the instructions
- When you have finished digitizing and clicked the end digitize button, give the new dataset a name, such as combined formula line.
- Right click the new line in the project, and select Table view
- 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.