1 adj. — Geography
from a more northern part of Vancouver Island.
Type: 3. Semantic Change — Up-island is used in other island locations and contexts. DARE lists the term as pertaining to the US Northeast, with a citation from 1885 referring to Martha's Vineyard, MA. Other uses in DARE refer to Long Island, NY (see DARE, s.v. "up island"). In Canada, and especially in British Columbia, the term is used attributively to refer to northern Vancouver Island.
See also COD-2, s.v. "up-island", which is marked "Cdn".
See also: down-island
2 adv. — Geography
north of one's present or usual location on Vancouver Island.
Type: 3. Semantic Change — In relation to meaning 1, use as an adverb of location has been documented throughout the 20th century. In the phrase "go up-island", the term is most prevalent in British Columbia (see Chart 1).
See also COD-2, s.v. "up-island", which is marked "Cdn".
Images:

Chart 1: Regional Domain Search, 24 May 2013