New Martim Vaz was an aquatic city located in the Atlantic Ocean on Earth.
Rishon Uxbridge and her husband Kevin, actually an immortal Douwd, lived in this city for most of their married life, until they moved to Rana IV in 2361. (TNG: "The Survivors")
This location was only mentioned in dialogue.
New Martim Vaz may be named after the island of Martim Vaz
, off the coast of Brazil