Did you know that as much as 60% of Holland lies below sea level? Do you ever wonder why the country isn't flooded and how people know how high to build the dikes? This is all related to the NAP (Normaal Amsterdams Peil) – a reference measurement of the city’s water level. The measurement is also known as the Amsterdam Ordnance Datum.
The NAP is the oldest measuring unit of its kind in the world and is based on the average sea level during the 17th century. The NAP was established in Amsterdam and today serves as a reference point in many parts of Europe.
Visit the unique NAP exhibition, located in the visitors centre at Amsterdam City Hall. Using models, photos and other visuals, the exhibition shows just how far Holland and Amsterdam lie below sea level. Delve into the history of the water levels and discover how measurement methods changed over the years. See what the exact zero level looks like and check the current water levels of the North Sea at IJmuiden and at Vlissingen, and learn about the water level during the disastrous 1953 floods in the Zeeland province.