Amsterdam Ordnance Datum
Amsterdam Level (as height reference point later Normal Amsterdam Peil, short NAP ) is a German term for the zero point of a height determination in Amsterdam, which was first mentioned in 1674.
The determination of the zero point was made by measuring the water level ( level ) of the IJ, an inlet of the former North Bay Zuiderzee, the Haarlemmermeer lock ( Haarlemmermeer Luis ) in Amsterdam in the period between 1 September 1683 to 1 September 1684th The zero point was the water level of the Middle high water ( MHW ) of this period selected. This water level was about 17 cm above the mean water ( 34 cm tidal range ). The amount was held by eight marble panels on which notches marked a height of 2.67 meters (9 feet and 5 thumbs ) above the zero point. At least one panel ( " Huddesteen " by Johan Hudde called ) has been preserved until today. By royal decree of zero on February 18, 1818 by William I as the starting point for the elevation data ( reference height ) was determined for the whole of the Netherlands. Later this height was taken as the starting reference also in some neighboring countries, for example, was derived in 1878 by Prussia for the normal peak in 1879, then the reference level over the sea level for the whole of Germany.
End of the 19th century was Amsterdam Peil (AP ) renamed to Normal Amsterdam Peil (NAP ). The European Union seeks to introduce a uniform reference amount for the whole of Europe. The height definition Normal Amsterdam Peil (NAP ) was taken as the zero point.
The water level in Amsterdam has ( eg the IJsselmeer ) long since changed by water construction, is why occasionally spoken of the " former Amsterdam Level ". The water level of the Amsterdam canals is today, for example, about 40 cm below the NAP datum. Meanwhile, no longer the original Mean high water ( MHW ) lies at the origin of the Amsterdam level, but currently the NAP zero at approximately the height of the central water ( MW) of the North Sea. The accuracy of the height definition is not affected. Since the zero point setting the altitude in principle of water level fluctuations is independent. On the dependence of a water level only the word level reminds behalf.
An exhibition of the Amsterdam level is now in the Town Hall ( stadhuis ) of Amsterdam. Three columns show the water level of the North Sea at IJmuiden, the current water level of the Westerschelde at Vlissingen and a water level of the flood disaster of 1953, which was in Vlissingen 4.55 meters above the zero point.