On 10 March 2009, President Gloria Macapagal-Arroyo signed a new law adjusting the Philippines' archipelagic baselines. Baselines are lines on a map, identified by coordinates, from which is measured the twelve-mile territorial sea, where, according to the United Nations Convention on the Law of the Sea (UNCLOS), a coastal state or an archipelagic state like the Philippines has sovereignty. The UNCLOS provides for a “contiguous zone”, with a maximum breadth of twenty-four miles from the baselines, where the coastal or archipelagic state enforces “its customs, fiscal, immigration or sanitary laws and regulations”. States also have an exclusive economic zone, measured up to 200 miles from the baselines, where they have “sovereign rights” to explore, exploit, conserve and manage the natural resources in the waters and on and beneath the seabed.

Significantly, the new Philippine law, in its title, indicates its purpose as mainly to amend the existing baselines act and “to define the archipelagic baselines of the Philippines”. It does not extend the baselines to the Spratlys or to Scarborough Shoal, both of which China and Vietnam claim in their entirety, while the Philippines claims a part of what are called the Spratlys and all of Scarborough Shoal.

Unfortunately, some observers and commentators think that the new law extends the baselines to encompass both the claimed area of the Spratlys and Scarborough Shoal. It does not. The contrary impression may have arisen from the fact that the first bill that would adjust the baselines, which Representative Antonio Cuenco filed in the House of Representatives in November 2007, would extend those baselines to parts of the Spratlys and Scarborough Shoal. The basepoints that the Cuenco-proposed baselines would connect would include twelve in the Spratlys area and six in Scarborough Shoal.

However, the Department of Foreign Affairs opposed this provision in the Cuenco bill.Instead, it backed, and President Arroyo endorsed, a Senate version that would limit the baselines to the main Philippine archipelago and declare a “regime of islands” for the land features in the areas of the Spratlys and Scarborough Shoal that Manila claims.