Geodesics, or surveying, supplies the fundamentals for depicting the surface of the earth with indication of positions and altitudes. With the aid of map projection, the three-dimensional surface of the earth can be transferred to a two-dimensional level.

Because the earth is not perfectly round, distortions are unavoidable with every image. For this reason, a specific projection has to be chosen which produces as little distortion as possible in the region to be depicted. 

Back in 1935 already, swisstopo decided in favour of conformal oblique cylindrical projection, which is still widely used in national map production today. By contrast, the Dufour and Siegfried maps were based on conical projection.

Geodetic position and height control point networks are used for practical surveying.

The fundamental point of the position control network is located in Bern, with coordinates E = 2,600,000 metres (east) and N = 1,200,000 metres (north). These coordinates are shown on the edge of printed maps.

The starting point for the Swiss height system is “Repère du Niton” in Geneva, with an altitude of 373.6 metres.

Topography

Additional steps are required on the basis of the geodetic fundamentals. An aircraft equipped with a high-resolution aerial camera photographs the landscape from above. Here, too, the resulting images are distorted and therefore have to be geo-referenced. Now the images can be evaluated with the aid of photogrammetry and subsequently used for preparing maps. 

Any existing unclear situations have to be verified directly on site.

The heights of the terrain and objects are calculated with a high degree of precision with the aid of laser scanning carried out from an aircraft.

The data obtained using this method are then processed into a three-dimensional dataset and where necessary are supplemented with data from other sources. The resulting landscape and height model forms the basis for map production.               

Cartography

Cartographers use the landscape model as the basis for preparing the national maps, which comprise topographic maps in both analogue and digital form (map data) and cover the whole of Switzerland, plus part of each neighbouring country. Periodical updates are carried out at least every six years.

Compositions are produced from the printed national maps as required. Here the arrangement of the sheets differs from that of the standard maps. For military purposes, swisstopo produces special maps upon consultation with the armed forces. Other types of map are produced within the framework of the applicable legal mandates, for example aerial and geological maps.