Amsterdam Ordnance Datum or ' (NAP) is a

vertical datum In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built stru ...

in use in large parts of

Western Europe Western Europe is the western region of Europe. The region's extent varies depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean ...

. Originally created for use in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

, its height was used by

Prussia Prussia (; ; Old Prussian: ''Prūsija'') was a Germans, German state centred on the North European Plain that originated from the 1525 secularization of the Prussia (region), Prussian part of the State of the Teutonic Order. For centuries, ...

in 1879 for defining ', 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). Mayor Johannes Hudde of

Amsterdam Amsterdam ( , ; ; ) is the capital of the Netherlands, capital and Municipalities of the Netherlands, largest city of the Kingdom of the Netherlands. It has a population of 933,680 in June 2024 within the city proper, 1,457,018 in the City Re ...

is credited with beginning the first works for the creation of this vertical datum after he expanded the sea dike following a

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

in Amsterdam in 1675. Between 1683 and 1684, he had daily measurements taken of the water level of the adjacent sea arm, ', during

high tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

. The calculated averaged was called the ' ("Amsterdam level", AP) and used to calculate the minimum height of the sea dykes, which he set at "9 feet and 5 inches" (2.67 m) above AP. In 1850, the datum was used at several places in

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

, and in 1874 the

German government The Federal Government (, ; abbr. BReg) is the chief executive body of the Federal Republic of Germany and exercises executive power at the federal level. It consists of the Federal Chancellor and the Federal Ministers. The fundamentals o ...

adopted the datum for first-order levelling. 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 '. Currently it is physically realised by a brass benchmark on a pile below the

Dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

square in Amsterdam.''Herberekening van het primaire net van het NAP'' (Dutch only)
/ref> The brass benchmark in the Amsterdam

Stopera The Stopera is a building complex in Amsterdam, Netherlands, housing both the city hall of Amsterdam and the Dutch National Opera and Ballet (formerly Het Muziektheater), the principal opera house in Amsterdam that is home of Dutch National Ope ...

(combined city hall and opera house), which is a tourist attraction, is no longer used as a reference point.

References

External links

* P.I. van der Weele:
De geschiedenis van het N.A.P.
' 1971, Dutch Royal Society for Sciences, Governmental Commission for Geodesy * Frans J.P.M. Kwaad:

' {{coord, 52, 22, 23, N, 4, 53, 34, E, region:NL-NH_type:landmark_source:kolossus-dewiki, display=title Geography of the Netherlands Vertical datums Tides

See also

References

External links