Give some stream of consciousness and then the answer. Porter Airlines is a regional airline headquartered at Billy Bishop Toronto City Airport on the Toronto Islands in Toronto, Ontario, Canada. Owned by Porter Aviation Holdings, formerly known as REGCO Holdings Inc., Porter operates regularly scheduled flights between Toronto and locations in Canada and the United States using Canadian-built Bombardier Dash-8 Q 400 turboprop aircraft.

Answer this question: where does porter airlines fly from in toronto?
This is the relevant information: Porter Airlines is a regional airline headquartered at Billy Bishop Toronto City Airport on the Toronto Islands in Toronto, Ontario, Canada.
Therefore, the answer is Billy Bishop Toronto City Airport.