According to the most recent Statistics Canada's National Economic Accounts, the Mining and Oil and Gas Extraction industry accounted for approximately 26% of Alberta's Gross Domestic Product (GDP) in 2020, an increase from 23.3% in 2010.
Say a town grows up around a single manufacturing plant. That plant might only account for 30% of the town's GPD because people use their wages to buy food, housing, etc. But when that plant closes up and 90% of the towns income disappears, it's hard to argue that the plant only contributed 30% of the economy in that case.
GPD != economy. GPD describes how money is spent, not necessarily in what order it is generated.
I suspect you need to collect reliable information on imports and exports and capital flows to calculate GDP, and a town can't collect it because it doesn't have, e.g., a customs bureacracy.
Yes, of course it does. Why wouldn't it?