Part 1 of the Tuvalu Maritime Zones Act 2012 states that the territorial sea comprises those areas of the sea having
(a) as their inner limits, the baseline, which is measured from the low-water line of the seaward side of the reef fringing the coast of any part of Tuvalu or bounding any lagoon waters adjacent to any part of that coast, or where a reef is not present, the low-water line of the coast itself and
(b) as their outer limits, a line measured seaward from that baseline, every point of which is distant 12 nautical miles from the nearest point of that baseline.
Where archipelagic baselines are declared, the territorial sea comprises those areas of the sea having –
(a) as their inner limits, the baseline, and
(b) as their outer limits, a line measured seaward from that baseline, every point of which is distant 12 nautical miles from the nearest point of that baseline.
In addition, the Declaration of Territorial Sea Baselines 2012 made under the MZA 2012 contains the geographical coordinate with reference to the World Geodetic System 1984 (WGS 84). Points are connected by geodesic lines realized in WGS84.
https://www.un.org/depts/los/LEGISLATIONANDTREATIES/PDFFILES/tuv_maritime_zones_act_2012_1.pdf
https://www.un.org/depts/los/LEGISLATIONANDTREATIES/PDFFILES/tuv_declaration_territorial_sea_baselines2012_1.pdf
