Published on: 17.9.2020
Information produced by Finnish Environment Institute
Height systems and the sea level
Land uplift, which results from the Earth’s crust being pressed down during the Ice Age, continues steadily in Finland. Rather than being stable, the sea level rises and falls constantly. In order to compare the heights of different locations, a baseline level for calculating heights must be agreed.
Height systems based on high-precision levelling have been used in Finland for more than a century. The first one, known as the NN system, remains in use for such purposes as decisions on water level regulation and depth data of lakes and rivers.
A second high-precision levelling in Finland was carried out in 1935–1975, and in its early stages, N43 was introduced as a temporary height system. Once the levelling had been completed, the national N60 system was introduced. It was corrected for land uplift in 1960 and remains in extensive use today.
Currently, the recommended system is the European N2000 system of heights corresponding with the land uplift in year 2000. While the N2000 system is based on the Amsterdam Ordnance Datum NAP, Finnish surveyors do not have to go all the way to Amsterdam to compare heights. A height value has been calculated for the Finnish N2000 datum point located at Metsähovi research station in Kirkkonummi, and the heights of all N2000 points in Finland have been determined in relation to it.
N2000 system heights differ from the previously used N60 heights by 13 to 43 centimetres, mainly because of correction for land uplift. This difference is most noticeable along Gulf of Bothnia coasts where the land is rising the most.
Image: © Ilkka Valli
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On external sites: Depth data and fairway information (Finnish Transport Infrastructure Agency)