Situated at the junction of three major waterways, Ottawa is located in the Ottawa valley. It lies on the south bank of the Ottawa River, where it meets the Rideau River and the Rideau Canal. Across the Ottawa River, which forms the border between Ontario and Quebec, lies the city of Gatineau, itself the result of amalgamation of the former Quebec cities of Hull and Aylmer together with Gatineau. Although formally and administratively separate cities in two separate provinces, Ottawa and Gatineau (along with a number of nearby municipalities) collectively constitute the National Capital Region.

Ottawa is approximately 400km (250 miles) east of Toronto and 190km (120 miles) west of Montreal.

Ottawa's latitude is 45.26'N and its longitude is 75.41'W. The city has approximately the same latitude as Venice (Italy), Bordeaux (France), Portland (Oregon), Sapporo (Japan). The area is 5318.36km2 (2053.43sq.mi.) and it is 80m (262ft) above sea level in the Eastern (EST) (UTC-5) time zone.

Close to the U.S. border, Ottawa is only a two hour flight away from over 200 million people.