In the Netherlands, the Normaal Amsterdams Peil (Normal Amsterdam Level) is the most used point of comparison. It’s an imaginary plane set at a certain height.
The fixed point for height and depth calculations is located on Dam Square in Amsterdam. There’s a concrete pile hit into the ground. In the head of this pole is a bronze bolt with a spherical top end. The highest point of this bolt head is at NAP + 1.4278 m and about 90 cm below the pavement.
In the Stopera in Amsterdam, the NAP has been made visible for several years now. There is an illuminated horizontal line there, which is exactly at NAP height. Three columns of water have also been placed. The highest column shows the water level of 1 February 1953 in the event of a flood disaster. In the other columns the water level is always different, because they indicate the varying water levels of Vlissingen and IJmuiden.
The largest part of the west and northwest of the Netherlands lies below sea level. In the Prins Willem Alexander polder near Rotterdam, the lowest point of the Netherlands is located at NAP – 6.60 m.
If a place is above NAP, this is indicated by the + (plus) sign. If a place is below NAP this is indicated by the – (min) sign.