The altitude of Polaris depends on where it is measured from. For example, when measured at the equator, it is located at 0' altitude. The altitude increases as the location moves north away from the equator; Polaris cannot be seen in the sky south of the equator.
The altitude of a star is its height above the horizon, which is equal to the observer's latitude. Therefore, people can calculate their latitude on Earth by measuring the distance of Polaris from the horizon. Since the Earth's axis points directly at Polaris, observers at the North Pole see Polaris located directly overhead.