Douglas is the capital city and largest settlement of the Isle of Man, with a population of 26,677 and an area of 4.1 square miles. It is located at t…Douglas is the capital city and largest settlement of the Isle of Man, with a population of 26,677 and an area of 4.1 square miles. It is located at the mouth of the River Douglas, and on a sweeping bay of two miles. The River Douglas forms part of the city's harbour and main commercial port.