For a tutorial on the edging from the designer visit: http://picnicknits.com/tutorial/tutorial-tuesday-cassian/
Cassian starts at the neck and moves out to the edge. It has a charted lace that is easy to add or subtract repeats. The final edging is done sideways, worked over the live stitches of the shawl as a bind-off.
This shawl is a rounded rectangular shape. The final measurements shown are 43" inches long and 21.5" deep. However, the shawl is very easy to make bigger or smaller, and you simply do more or less repeats of the main lace pattern. The yardage given is for the measurements given, but will go up or down if you change the size.
Sample is shown in Pigeonroof Studios Siren Two Sock. A suggested substitute is shown below.