Canada is located in the northern hemisphere by latitudinal measurements and in the western hemisphere by longitudinal measurements. Because a small portion of Alaska's Aleutian Islands extends into the eastern hemisphere, Canada is the largest country entirely contained in this quarter of the globe.
Earth is divided into northern and southern hemispheres at the equator and into eastern and western hemispheres at the Prime Meridian and the Antimeridian. While the equator is a natural division easily measured using seasonal changes, the meridians were arbitrarily chosen. The Prime Meridian, which runs through Greenwich, England, was defined at the International Meridian Conference in 1884, according to The Greenwich Meridian website.