Why it's the capital
Nauru's Parliament House and main government offices are in Yaren, so it serves as the capital in practice. The United Nations accepts it as Nauru's 'main district'.
Capital of NauruYaren is a small district of about 1.5 km² on the south coast of Nauru, a single island just south of the equator. Its neighbours are Buada to the north, Meneng to the east and Boe to the west.
Nauru's Parliament House and main government offices are in Yaren, so it serves as the capital in practice. The United Nations accepts it as Nauru's 'main district'.
Look just south of the equator, west-south-west of Tarawa in Kiribati. Nauru is a single small island there, and Yaren is on its southern shore.
Nauru has no official capital and no cities, so some maps leave the capital out; Yaren is the de facto capital.
Sources: Wikipedia: Yaren District