# Swiss coordinate system

(Redirected from CH1903)

The Swiss coordinate system (or Swiss grid) is a geographic coordinate system used in Switzerland for maps and surveying by the Swiss Federal Office of Topography (Swisstopo).

The map projection used is Oblique Mercator on an 1841 Bessel ellipsoid.

The geodetic datum CH1903 (SRID 21781) uses as fundamental point the old observatory of Bern (46°57′3.9″N 7°26′19.1″E﻿ / ﻿46.951083°N 7.438639°E (WGS84)), the current location of the Institut für exakte Wissenschaften of the University of Bern. In order to avoid errors during coordinate transmissions, the coordinates of this point are 600'000 m E / 200'000 m N. The 0 / 0 coordinate is located near Bordeaux, France. Though E coordinate is denoted as y and N coordinate x, E coordinate is the first axis of this Cartesian system, namely a point is denoted as (y, x). As an example, the observatory is (600'000, 200'000). This definition invokes the following effects:

• All coordinates are always positive, since Switzerland is located in the 1st quadrant of the coordinate system.
• Furthermore, the whole area of Switzerland is located below the y=x line of the coordinate system. Thus, all E-coordinates are always bigger than N-coordinates.

The CH1903+ datum is a refinement and improvement of CH1903. It is based on WGS84, and it was devised for the national land survey of 1995 (LV 95 for Landesvermessung 1995). The coordinates of its new reference point, the Zimmerwald Observatory, should maintain the CH1903 coordinates as far as possible - the maximum shift between the two datums is 3 metres on the ground, so most map and GPS users will not notice any difference. The easting and northing is increased by 2 and 1 million, respectively, resulting in 14-digit rather than 12-digit metre coordinates.

CH1903 CH1903+ y = 602 030.68 m x = 191 775.03 m E = 2 602 030.74 m N = 1 191 775.03 m