From the Wikipedia page 
Gästrikland (help·info) is a historical province or landskap on the eastern coast of Sweden. It borders Uppland, Västmanland, Dalarna, Hälsingland and the Gulf of Bothnia. Gästrikland is the southernmost of the Norrland provinces.
Other used forms of the name is Gestricia, Gastrikland. Before 1900, the spelling was officially Gestrikland in Swedish.