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Geological maps

What is a geological map?

A geological map gives information on the superficial layers of the Earth’s crust. The geological formations are listed according to their composition (lithology), their age (stratigraphy) and their structural position (tectonic). They are placed on a topographic base (map) using different graphic elements (symbols, figuratives and colors). The choice of scale depends on the geological content and the intended objective of the map.

How are geological maps made?

 
Swiss geological sketch

The essential condition for establishing a geological detail map is a precise field survey, based on numerous measurements and observations. The topographic base is generally taken from maps at a scale of
1:10 000, such as those of the comprehensive cadastral plans.

The field geologist determines the rock type according to various criteria and measures its orientation. All data are transcribed onto the map and in a field notebook. Besides the natural or artificial outcrops, data from bore holes or important test holes are taken into consideration.
In the case of a doubtful rock identification, complementary investigations are carried out in the laboratory on samples of these rocks.
At the end of the field survey, the geologist establishes an original draft at a scale of
1:25 000 and constructs some geological sections across the studied sector. He also writes an explanatory note that generally contains numerous illustrations.
The geological cartography section assures the direction of the project, carries out the editing of the map, establishes the final legend of the map and provides indispensable data for the cartographers.

Publishing geological information

Professional carographers carry out the cartographic work in close collaboration with the Swiss National Geological Survey.
The original geological map is scanned by the cartographic division. This document serves as a background for the manual digitisation of geological information on the screen.
The colours of the surfaces are decided during the editing phase. Between 12 and 16 base colours are used for any given sheet of the Geological Atlas, depending on the number of geological formations present.
The printing plates are then produced. The definitive colours are adjusted on the rotary press at the time of the printing of proofs and editions. About 1500 to 3000 copies of the maps are printed on robust paper.

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Contact

Swiss Geological Survey Secretariat
Seftigenstrasse 264
CH-3084 Wabern

Tel +41 58 469 05 68
Fax +41 58 469 05 45

e-mail to the secretariat
web: Swiss Geological Survey

 

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