This network is the origin for most height determinations in Swiss maps and for all surveys carried out in Switzerland. It comprises 18 primary loops and additional secondary lines with a total of about 8000 bench marks (bolts) spaced 1 to 2 km along the main roads in Switzerland. The heights of these bench marks are the official heights (without gravity reduction) for Switzerland and are available in the form of continually revised lists.
The repeated measurements of the national levelling network have shown a relative uplift of the Alps of up to 1.5 mm/year with respect to the Swiss Plateau. Therefore, the (static) values which have been held fixed up to today are no longer representative in national surveying. Furthermore, disregarding the effects of gravity results in systematic differences to a potential-theoretic rigorous height system. For these reasons it was decided to establish the new national vertical reference system LHN95.
