The expansion is based on internationally established definitions of the continental shelf, and comes from research and surveys conducted by various groups going back to 2003, confirming where the continental shelf actually is.

Interestingly, this doesn’t include the water column above this territory, so it doesn’t mean control of fishing or shipping lanes. Only seabed/underground mineral/drilling/pipelines control. Depending on policy and which political party is in control at the time, this could mean preventing others from drilling these areas, or (more likely?) making a profit off allowing drilling here.

Most of the addition is in the Arctic, but includes territory around the whole country.