Atiu Island is not a city, but rather an island located in the Cook Islands in the South Pacific Ocean. It is part of the Aitutaki Island Group in the southern grouping of the Cook Islands. The main settlement on Atiu Island is called Teenui, and it serves as the administrative center for the island. However, it is important to note that Atiu Island is not classified as a city since it has a relatively small population and is primarily rural in nature.