The last remaining in situ Hudde benchmark in the Eenhoorn lock in Amsterdam
Amsterdam Ordnance Datum or Normaal Amsterdams Peil (NAP) is a vertical datum in use in large parts of Western Europe. Originally created for use in the Netherlands, its height was used by Prussia in 1879 for defining Normalnull, and in 1955 by other European countries. In the 1990s, it was used as the reference level for the United European leveling Network (UELN) which in turn led to the European Vertical Reference System (EVRS).[1]
Mayor Johannes Hudde of Amsterdam in a way came up with the idea after he expanded the sea dike after a flood in Amsterdam in 1675. Of course a dike should be storm-resistant to protect a city against flooding, and in this case a margin of "9 feet and 5 inches" (2.67 m - margin is defined in Amsterdam feet) was deemed enough to cope with rising water. So he measured the water level of the adjacent sea arm, Het IJ, and compared it with the water level in the canals within the city itself. He found that the water level at an average summer flood in the sea arm (when the water level reaches its maximum, not counting storms) was about the same as the level on the other side of the sea-dike, plus the margin of 9 feet and 5 inches. In 1850, the datum was used at several places in Belgium, and in 1874 the German government adopted the datum for first-order levelling.[2]
The relatively constant water level in the canals of Amsterdam, called Amsterdams Peil ("Amsterdam level", AP), was equal to the level at summer flood at sea in the sea-inlet, which changes throughout the year. AP was carried over to other areas in the Netherlands in 1860, to replace locally used levels. In this operation, an error was introduced which was corrected (normalised) between 1885 and 1894, resulting in the Normaal Amsterdams Peil.
Originally the zero level of NAP was the average summer flood water level in the IJ just north of the centre of Amsterdam (which was at the time, in 1684, the main shipping area, then still connected with the open sea). Currently it is physically realised by a brass benchmark on a 22-metre (72 ft) pile below the Dam square in Amsterdam.[3] The brass benchmark in the Amsterdam Stopera (combined city hall and opera house), which is a tourist attraction, is no longer used as a reference point.
^"European Vertical Reference System". bund.de. Retrieved 9 July 2015.
^van der Weele, P. I. (1971). "De geschiedenis van het N.A.P." [The history of the N.A.P.]. Publication of the Netherlands Geodetic Commission (Rijkscommissie voor Geodesie) (in Dutch). ISBN 9061320224.
^Herberekening van het primaire net van het NAP (Dutch only)
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point of the Netherlands: 6.76 m (22.2 ft) below AmsterdamOrdnanceDatum (mean summer sea level in Amsterdam). It is the hometown of Miss Universe 1989, Angela...
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longest running sea-level measurements, NAP or AmsterdamOrdnanceDatum were established in 1675, in Amsterdam. Record collection is also extensive in Australia...
metres (1 ft 4 in) below the AmsterdamOrdnanceDatum. If ice forms in winter, there is a possibility of skating on the Amsterdam canals. Waternet will stop...
canals in the city center, is -0.40 metres (1 ft 4 in) from the AmsterdamOrdnanceDatum. The Herengracht in The Hague is filled in. Maarssen also has a...
vertical datums, such as the NAVD 88 (North American Vertical Datum 1988), NAP (Normaal Amsterdams Peil), the Kronstadt datum, the Trieste datum, and numerous...
according to the Normalhöhennull levelling system based on the AmsterdamOrdnanceDatum Italy: −0.5 to −3.2 cm, orthometric height referring to Genoa Tide...
de Vrouweheide, built in 1858, is located at 216 meters above AmsterdamOrdnanceDatum, and built on an artificial hill to catch even more wind. As such...
barrier is closed at an anticipated water level of 2.25 metres above AmsterdamOrdnanceDatum (NAP). Closure of the barrier takes between 20 and 60 minutes....
It would become 110 m long, 18.20 m wide and 7.33 m deep below AmsterdamOrdnanceDatum and was finished on 15 December 1864. Other recommendations of...
and it is dredged to a depth of 14.5–16 metres (48–52 ft) below AmsterdamOrdnanceDatum. It is this channel, together with the dredged channels in the...
Retrieved 1 December 2013. "Wat is het Normaal Amsterdams Peil (NAP)?" [What is the AmsterdamOrdnanceDatum]. rijksoverheid.nl (in Dutch). Government of...
destroy Zaamslag village and its castle, because both were above AmsterdamOrdnanceDatum. However, neglect by abandonment would have the same effect. In...
line') over the Plaat van Oude Tonge is 5.5 metres above AmsterdamOrdnanceDatum (Normaal Amsterdams Peil, NAP). This high crest line is necessary due to...
Kaiser Wilhelm I. on 22 March 1879. This point was derived from the AmsterdamOrdnanceDatum and marked off 37 meters over zero. Wilhelm Foerster led the observatory...
's-Hertogenbosch the railroad would be constructed at 7.5 m above AmsterdamOrdnanceDatum. It meant that it would be constructed on a railroad dyke. Two...
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