Utrecht is the centre of a densely populated area, which makes concise definitions of its agglomeration difficult, and somewhat arbitrary. The smaller Utrecht agglomeration of continuously built up areas counts some 420,000 inhabitants and includes Nieuwegein, IJsselstein and Maarssen. It is sometimes argued that the close by municipalities De Bilt, Zeist, Houten, Vianen, Driebergen-Rijsenburg (Utrechtse Heuvelrug), and Bunnik should also be counted towards the Utrecht agglomeration, bringing the total to 640,000 inhabitants. The larger region, including slightly more remote towns such as Woerden and Amersfoort counts up to 820,000 inhabitants.