of the Nieuwe Maas, although recent urban development has extended the centre to parts of southern Rotterdam known as Kop van Zuid ('the Head of South', i.e. the northern part of southern Rotterdam). From its inland core, Rotterdam reaches the North Sea by a swathe of predominantly harbour area. Built mostly behind dikes, large parts of the Rotterdam are below sea level. For instance, the Prins Alexander Polder in the northeast of Rotterdam extends below sea level, or rather below Normaal Amsterdams Peil (NAP) or 'Amsterdam Ordnance Datum'. The lowest point in the Netherlands ( below NAP) is situated just to the east of Rotterdam, in the municipality of Nieuwerkerk aan den IJssel. The Rotte river no longer joins the Nieuwe Maas directly. Since the early 1980s, when the construction of Rotterdam's second subway line interfered with the Rotte's course, its waters have been pumped through a pipe into the Nieuwe Maas via the Boerengat. Between the summers of 2003 and 2008, an artificial beach was created at the Boompjeskade along the Nieuwe Maas, between the Erasmus Bridge and the Willems Bridge. Swimming was not possible, digging pits was limited to the height of the layer of sand, about . Alternatively, people go to the beach of Hook of Holland (which is a Rotterdam district) or one of the beaches in Zeeland: Renesse or the Zuid Hollandse Eilanden: Ouddorp, Oostvoorne. Rotterdam forms the centre of the Rijnmond conurbation, bordering the conurbation surrounding The Hague to the north-west. The two conurbations are close enough to be a single conurbation. They share the Rotterdam The Hague Airport and a light rail system called RandstadRail. Consideration is being given to creating an official Metropolitan region Rotterdam The Hague (Metropoolregio Rotterdam Den Haag), which would have a combined population approaching 2.5 million. On its turn, the Rijnmond conurbation is part of the southern wing (the Zuidvleugel) of the Randstad, which is one of the most important economic and densely populated areas in the north-west of Europe. Having a population of 7.1 million, the Randstad is the sixth-largest urban area in Europe (after Moscow, London, Paris, Istanbul, and the Rhein-Ruhr Area). The Zuidvleugel, situated in the province of South Holland, has a population of around 3 million. Climate Rotterdam experiences a temperate oceanic climate (Köppen climate classification Cfb) similar to all of the coastal areas in the Netherlands. Located near to the coast, its climate