France adopted four decrees in September 2015 that redefined the external limits of its continental shelf (the seabed and the soil under the seabed that can be included in a country’s landmass).
Exclusive Economic Zones (EEZ), which grant special rights to resources such as fishing and mineral extraction in an area extending 200 nautical miles (370km) from a country’s coast, are enshrined in the 1982 United Nations Convention on the Law of the Sea, which has been ratified by 167 countries.
Article 76 deals with the continental shelf, not the EEZ. The continental shelf's constrained maximum, if other criteria are met, is either 350 nautical miles or 100 nautical miles beyond the 2500m isobath, whichever gives the best result. The EEZ can only extend to a maximum of 200 nautical miles (thanks Stuart Kaye for a technical correction). But it only applies to the seabed and so excludes fishing rights. France demonstrated an increase was appropriate to its territories of French Guiana, Martinique, Guadeloupe, New Caledonia and the Kerguelen Islands, adding a total of 579,000 square km to its surface area.
These special areas are potentially very valuable so there are plenty of disputes. There are many dual claims on territorial waters such as France’s claim around Saint-Pierre-et-Miquelon, which is surrounded by Canada’s EEZ. Canada and America have overlapping claims in the Beaufort Sea. In the South China Sea tension has risen over disagreements between China and several neighbouring countries. With the oceans covering 140 million square miles (226 million square km) of the Earth's surface, around a third of which are EEZs, there is plenty up for grabs. It is unlikely to be plain sailing any time soon.
The Imperial Residues
Since 1946, the United Nations has compiled a list of the world's “Non-Self-Governing Territories”: overseas domains it considers, in effect, to be colonies. Since then 100-odd entries have come and gone. Leavers may gain full independence (such as Cameroon or Singapore) or merge more or less fully with their parent nation (Puerto Rico or French Guiana). Today the number of entries has dwindled to just 15, most of which are British, or 16 if you include ambiguous Western Sahara.
The UN lists only inhabited territory. A host of other, unpopulated, territories would be open to scrutiny on grounds of proximity, or lack of it: swathes of Antarctica for example. Norway's Bouvet Island in the South Atlantic is the most remote island on the planet, lying furthest from any other land mass. But at a meagre 12,700 km from Oslo it cannot compete with some inhabited British, French or American islands for the furthest distance from the motherland.