The Randstad is a conurbation in the western Netherlands. It covers the provinces of North Holland, South Holland, Flevoland and Utrecht. Big cities in the Randstad are Amsterdam, Haarlem, Leiden, Den Haag, Delft, Rotterdam, Dordrecht, Gouda, Utrecht, Hilversum and Almere. The term Randstad was first used by Albert Plesman, the founder of KLM. When he looked at it from the air, he saw that cities nearly form a circle. The Randstad covers about 20% of the area of the Netherlands. More than 40% of the population of the Netherlands live there. The cities in the Randstad are between 26 kilometres (16 mi) (Den Haag - Rotterdam) and 77 kilometres (48 mi) (Amsterdam - Rotterdam) apart. In the center is an area known as Groene Hart. Relatively few people live there.