I am working on this maritime boundary shape file for India, which extends 200 nautical miles ( 1 nm = 1.15 miles) from the land boundary. On some areas, the maritime boundary will be shorter as well.
What I would like to do is, instead of 200 nm extension, I would like to create a new boundary for the maritime area, that is 68 kms from the land boundary. For the areas that is already shorter than this 68 kms, I would like to keep the already existing area.
I have attached a copy of the shape file for maritime boundary along with India's land boundary with this post for your kind verification please. Area in the red is the maritime boundary and the area in yellow is the land.