Suchergebnisse

Throughout history, the still surface of the sea has been used as a reference for heights and elevations. A given landmark's "height above sea Ievel" is the distance measured in a plumb line from the Iandmark itself to the surface of the sea, which continues beneath the surface of the continents. Until the mid nineteenth century, the topographical surveying of countries did not include the measurement of elevations. This practice only ensued after the mean sea Ievel of each country was determined at nearby coastal tide gauging sites and marked by permanent bench marks. The mean sea Ievel at a tide gauging site is influenced by several factors including tides, currents and winds. As it is difficult to monitor these influences, the mean sea Ievels of different countries vary somewhat. Landlocked countries must base their national elevation systems upon the Ievel datums supplied by neighbouring countries. The development of the German national elevation system and the ways in which it differs from those of its neighbours as well as from standardised European systems are described in detail.