Until 1900 Rijswijk remained a relative small community but it became urbanized during the 20th century when it expanded rapidly. Today, Rijswijk's area has almost been completely built-up. The last major development is the new Ypenburg neighbourhood, built on the lands of the former Ypenburg Airfield but this part of Rijswijk was annexed by The Hague in 2002. Rijswijk is part of the Haaglanden conurbation. During the years its built-up area has grown to the point where it has effectively merged with The Hague, even though it is still a separate municipality.