Tricity (or Tri-City, also called Treble City, in Polish Trójmiasto) is an urban area consisting of three Polish cities: Gdańsk, Gdynia and Sopot. They are situated adjacent to one other, in a row, on the coast of the Gdańsk Bay, Baltic Sea, in Eastern Pomerania (Pomeranian Voivodeship), northern Poland. The Tricity metropolitan area has a population of over 1 million people. The name Trójmiasto was used informally or semi-formally only, until 28 March 2007, when "Tricity Card" (in Polish "Karta Trójmiasta") was signed as a declaration of cities' cooperation.