Topographic Map of Switzerland

This article is about the historical map. For modern maps, see National Maps of Switzerland.

The Topographic Map of Switzerland (German: Topographische Karte der Schweiz), also known as the Dufour Map (German: Dufourkarte; French: Carte Dufour) is a 1:100 000 scale map series depicting Switzerland for the first time based on accurate geometric measurements. It is also the oldest official map series of Switzerland.

Bern as depicted on the Dufour Map

The Atlas Suisse as predecessor

From 1796 to 1802, the Atlas Suisse was published in Aarau by Johann Heinrich Weiss, Johann Rudolf Meyer and Joachim Eugen Müller.

The Atlas Suisse map series consisted of 16 sheets, was produced by a copperplate or intaglio printing process, and depicted the whole of Switzerland at a scale of 1:120,000.

The Dufour Map

The Dufour Map depiction of Lausanne

In the 19th century in particular, learned societies contributed to the emergence of national consciousness and the emancipation of the bourgeoisie. Their members, who often held influential positions, formed a link between citizens and the administration. The societies carried out public tasks and brought together people of different faiths and backgrounds. They offered scholars the opportunity to freely exchange their ideas outside of academia.^[1] During the period of Geneva's annexation to France (1798-1813), the Société des Naturalistes took the name of Société de Physique et d'Histoire Naturelle (SPHN). Respectively since 1801 and 1805, Alessandro Volta and Alexander von Humboldt were honorary members of the SPHN. Henri-Albert Gosse, its founder in 1791,^[2] was also behind the creation of the Swiss Academy of Natural Sciences, the first of its kind in Europe, in 1815.^[3][4] In the same year, Switzerland expanded from 19 to 22 cantons with the accession of the cantons of Geneva, Neuchâtel and Valais. Guillaume-Henri Dufour, cantonal engineer in Geneva since 1817 and commissionned by the Federal Diet to superintend land surveying of Switzerland,^[5][6] founded in 1838 in Carouge (canton of Geneva) a topographic office (the future Federal Office of topography),^[7] which published under his direction, from 1845 to 1864, the first official map of Switzerland, on the basis of new cantonal measurements.^[8][9] The map of the canton of Geneva, which can be considered Dufour's masterpiece, had been published in 1842.^[10] After the Sonderbund War, the country pacified by Guillaume-Henri Dufour adopted a new Swiss Federal Constitution, inspired by the Constitution of the United States,^[11] founding the federal state in 1848.^[12]

Primordial triangulation of Switzerland (1826-1837).

Officers of the General Staff took over the initial work carried out during the time of the Helvetic Republic and their first topographical surveys of Switzerland were carried out from 1809. However, it was not until 1832 with the appointment of Dufour as head of the General Staff that the national map project took shape.^[13] Dufour's work enabled the Swiss Confederation to have a valuable tool for its army and administration. Some surveys for the map had been conducted by the Cantons, but the federal government had made its contribution by tracking data in mountainous areas with difficult access. Between 1834 and 1837, Johannes Eschmann connected and remeasured several existing cantonal networks to form the first national triangulation, which included the regions north of the Alps and those to the south. In 1840, Eschmann published the results of his work, which were used as the geodetic reference system for the Dufour Map.^[13][14]

The map projection adopted by the commission was the Bonne projection, centred on the Bern Observatory (5° 6' 10.8'' east of Paris meridian), although this point was much closer to the western end of Switzerland than to its eastern end. But its position was well known, and there was no more central observatory. The scale was set at 1:100 000 because it was considered more suitable for a country as rugged as Switzerland than the 1:80 000 adopted for the large map of France and the two maps were in any case inconsistent, as the meridians of the map of Switzerland tilted in the opposite direction to those of the map of France. The map commission wanted to adopt decimal measures; and Switzerland did not have an already existing map which, like the Cassini map, used a scale close to 1:86 400, i.e. 1 line (1⁄12 of a French inch) to 100 toises (i.e. 600 French feet). The metre was adopted as a linear measure, and the entire map was divided into twenty-five sheets: five east–west and five north–south. Each sheet of the map showed two scales, one purely metric, the other in Swiss leagues 4,800 metres in length. The frame was divided into sexagesimal minutes and centesimal minutes; the latter, each subdivided into ten parts, had the advantage of showing Kilometres in the direction of the meridians; so that there were new scales on the sides of the sheet to evaluate the distances.^[15][16]

The original images for the Dufour Map were created in 1:25,000 scale (for the Swiss plateau) and 1:50,000 (for the mountains). However, the Dufour Map was published in 1:100,000 scale, enabling the territory of Switzerland to be divided into 25 sheets, each of which measured 70 centimetres (28 in) x 48 centimetres (19 in). Publication of the Dufour Map was begun in 1845 by the Federal Topographic Bureau under Guillaume-Henri Dufour, and continued to December 1864. The Dufour Map was based on measurements by the Cantons and the Swiss Confederation.^[13] The Dufour Map was reproduced by an engraving print process, initially by intaglio, and later (from 1905) by flat plate impression. Until 1939, there were occasional revised editions of the Dufour Map sheets. The initially monochromatic map was enhanced in 1908 by the addition of an extra color, and then in 1938 by yet another colour.

The Dufour map at 1:100,000 engraved on copper, suggested the relief by hatching and shadows.^[8] The countryside (which in Switzerland is mostly hilly or mountainous) is depicted on the Dufour Map with hachures, which makes it appear especially vivid. Relief and elevation differences under the surface of lakes were symbolized by contours. This so-called "Swiss style" depiction received much praise, and earned the Topographic Bureau several international awards.^[13]

The Dufour Map also conveys a precise idea of Swiss geography of the second half of the 19th century and the early 20th century. One can see villages that have disappeared, glaciers that have retreated, and names of mountains that have changed since that time. Different editions of the Dufour Map give a reliable overview of demographic trends in Switzerland, the extension of settlements and significant changes in the territory, such as the damming of rivers, the construction of roads, and railway development.

The legacy of the Dufour Map

The Dufour map (French: Carte Dufour), the first topographic map of Switzerland for which the metre was adopted as the unit of length, won the gold medal at the 1855 Paris Exposition.^[14][17] However, the baselines for this map were measured in 1834 with three toises long measuring rods calibrated on a toise made in 1821 by Jean Nicolas Fortin for Friedrich Georg Wilhelm von Struve.^[18][19] On the sidelines of the Exposition Universelle (1855) and the second Congress of Statistics held in Paris, an association with a view to obtaining a uniform decimal system of measures, weights and currencies was created. Under the impetus of this association, a Committee for Weights and Measures and Monies (French: Comité des poids, mesures et monnaies) would be created during the 1867 Paris Exposition and would call for the international adoption of the metric system.^[20]

In Europe, except Spain, surveyors continued to use measuring instruments calibrated on the Toise of Peru.^[20][21] Among these, the toise of Bessel and the apparatus of Borda were respectively the main references for geodesy in Prussia and in France. These measuring devices consisted of bimetallic rulers in platinum and brass or iron and zinc fixed together at one extremity to assess the variations in length produced by any change in temperature. The combination of two bars made of two different metals allowed to take thermal expansion into account without measuring the temperature.^[22][23] In order to avoid the difficulty in exactly determining the temperature of a bar by the mercury thermometer, Friedrich Wilhelm Bessel, inspired by Jean-Charles de Borda, introduced in 1834 near Königsberg a compound bar which constituted a metallic thermometer. A zinc bar was laid on an iron bar two toises long, both bars being perfectly planed and in free contact, the zinc bar being slightly shorter and the two bars rigidly united at one end. As the temperature varied, the difference of the lengths of the bars, as perceived by the other end, also varied, and afforded a quantitative correction for temperature variations, which was applied to reduce the length to standard temperature. During the measurement of the base line the bars were not allowed to come into contact, the interval being measured by the insertion of glass wedges. The results of the comparisons of four measuring rods with one another and with the standards were elaborately computed by the method of least-squares.^[24]

The Struve Geodetic arc measurement extended on a period of forty years and initiated an international scientific collaboration between Russian Empire and the United Kingdoms of Sweden and Norway with the involvement of proeminent astronomers such as Friedrich Georg Wilhelm von Struve, Friedrich Wilhelm Bessel, Carl Friedrich Gauss and George Biddell Airy.^[25] A French scientific instrument maker, Jean Nicolas Fortin, made three direct copies of the Toise of Peru, one for Friedrich Georg Wilhelm von Struve, a second for Heinrich Christian Schumacher in 1821 and a third for Friedrich Wilhelm Bessel in 1823. In 1831, Henri-Prudence Gambey also realised a copy of the Toise of Peru which was kept at Altona Observatory.^[26][21]

In the second half of the 19th century, the creation of the Central European Arc Measurement (German: Mitteleuropäische Gradmessung) would mark, following Carl Friedrich Gauss,^[27][20] Friedrich Wilhelm Bessel and Friedrich Georg Wilhelm von Struve examples,^[28] the systematic adoption of more rigorous methods among them the application of the least squares in geodesy.^[29][30] It became possible to accurately measure parallel arcs, since the difference in longitude between their ends could be determined thanks to the invention of the electrical telegraph.^[19] Furthermore, advances in metrology combined with those of gravimetry have led to a new era of geodesy. If precision metrology had needed the help of geodesy, the latter could not continue to prosper without the help of metrology. It was then necessary to define a single unit to express all the measurements of terrestrial arcs and all determinations of the gravitational acceleration by means of pendulum.^[31]

In 1866, an important concern was that the Toise of Peru, the standard of the toise constructed in 1735 for the French Geodesic Mission to the Equator, might be so much damaged that comparison with it would be worthless,^[19] while Bessel had questioned the accuracy of copies of this standard belonging to Altona and Koenigsberg Observatories, which he had compared to each other about 1840.^[32] In fact, the length of Bessel's Toise, which according to the then legal ratio between the metre and the Toise of Peru, should be equal to 1.9490348 m, would be found to be 26.2·10^-6 m greater during measurements carried out by Jean-René Benoît at the International Bureau of Weights and Measures. It was the consideration of the divergences between the different toises used by geodesists that led the European Arc Measurement (German: Europäische Gradmessung ) to consider, at the meeting of its Permanent Commission in Neuchâtel in 1866, the founding of a World Institute for the Comparison of Geodetic Standards, the first step towards the creation of the International Bureau of Weights and Measures.^[33][34] Spain joined the European Arc Measurement at this meeting.^[35] In 1867 at the second General Conference of the European Arc Measurement held in Berlin, the question of international standard of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth.^[36] The conference recommended the adoption of the metric system (replacing Bessel's toise) and the creation of an International Metre Commission.^[36]

Ibáñez apparatus calibrated on the metric Spanish standard and used at Aarberg, in canton of Bern, Switzerland in 1880.^[37][38]

From 1865 to 1868, Carlos Ibáñez e Ibáñez de Ibero added the survey of the Balearic Islands with that of the Iberian Peninsula.^[39] For this work, he devised a new instrument.^[40] This device, called the Ibáñez apparatus, would be used in Switzerland to measure the geodetic bases of Aarberg, Weinfelden and Bellinzona.^[38] Carlos Ibáñez e Ibáñez de Ibero recognized that the end standards with which the most perfect devices of the eighteenth century and those of the first half of the nineteenth century were still equipped, that Jean-Charles de Borda or Friedrich Wilhelm Bessel simply joined measuring the intervals by means of vernier callipers or glass wedges,^[40] would be replaced advantageously for accuracy by microscopic measurements, a system designed in Switzerland by Ferdinand Rudolph Hassler and Johann Georg Tralles,^[41] and which Ibáñez ameliorated using a single standard with lines marked on the bar.^[42]

Swiss Geodetic Commission

Gravimeter with variant of Repsold-Bessel pendulum

The Swiss Geodetic Commission was created during the publication of the Dufour map, and its initial work contributed to the design of the Topographic Atlas of Switzerland. In 1861, Johan Jacob Baeyer proposed the creation of the Central European Arc Measurement, whose objective was to redetermine anomalies in the shape of the Earth using precise geodetic surveys combined with gravimetry. The aim was to figure out the geoid using gravimetric and leveling measurements to derive an accurate understanding of the Earth ellipsoid while taking vertical deflections into account.^[43]

On July 7, 1861, the Prussian delegation in Bern submitted Baeyer's project to the Federal Council. The Federal Department of the Interior submitted it to Guillaume Henri Dufour, head of the Swiss Federal Office of Topography. At the 1861 session of the Swiss Society of Natural Sciences in Lausanne, the project discussed by the physics section of the Society was strongly supported by Élie Ritter and Adolphe Hirsch. On their proposal, the Society decided to give a favorable opinion on Switzerland's accession to the Central European Arc Measurement and to establish the Swiss Geodetic Commission. Its founding members were Rudolf Wolf, president (canton of Zurich), Guillaume Henri Dufour, honorary president and Élie Ritter, soon replaced by Émile Plantamour (canton of Geneva), Adolphe Hirsch (canton of Neuchâtel) and Hans Heinrich Denzler (canton of Bern).^[43]

In 1859, Friedrich von Schubert demonstrated that several meridians had not the same length, confirming an hypothesis of Jean Le Rond d'Alembert. He also proposed an ellipsoid with three unequal axes.^[44][45] In 1860, Elie Ritter, a mathematician from Geneva, using Schubert's data computed that the Earth ellipsoid could rather be an ellipsoid of revolution accordingly to Adrien-Marie Legendre's model.^[46] However, the following year, resuming his calculation on the basis of all the data available at the time, Ritter came to the conclusion that the problem was only resolved in an approximate manner, the data appearing too scant, and for some affected by vertical deflections, in particular the latitude of Montjuïc in the French meridian arc.^[47]

As early as 1861, Johann Jacob Baeyer sent a memorandum to the King of Prussia recommending international collaboration in Central Europe with the aim of determining the shape and dimensions of the Earth. At the time of its creation, the association had sixteen member countries: Austrian Empire, Kingdom of Belgium, Denmark, seven German states (Grand Duchy of Baden, Kingdom of Bavaria, Kingdom of Hanover, Mecklenburg, Kingdom of Prussia, Kingdom of Saxony, Saxe-Coburg and Gotha), Kingdom of Italy, Netherlands, Russian Empire (for Poland), United Kingdoms of Sweden and Norway, as well as Switzerland. The Central European Arc Measurement created a Central Office, located at the Prussian Geodetic Institute, whose management was entrusted to Johann Jacob Baeyer.^[48][49][50]

Baeyer's goal was a new determination of anomalies in the shape of the Earth using precise triangulations, combined with gravity measurements. This involved determining the geoid by means of gravimetric and leveling measurements, in order to deduce the exact knowledge of the Earth spheroid while taking into account local deflections of the plumb line due to gravity anomalies affecting gravity of Earth. To resolve this problem, it was necessary to carefully study considerable areas of land in all directions. Baeyer developed a plan to coordinate geodetic surveys in the space between the parallels of Palermo and Christiana (Oslo) and the meridians of Bonn and Trunz (German name for Milejewo in Poland). This territory was covered by a triangle network and included more than thirty observatories or stations whose position was determined astronomically. Bayer proposed to remeasure ten arcs of meridians and a larger number of arcs of parallels, to compare the curvature of the meridian arcs on the two slopes of the Alps, in order to determine the influence of this mountain range on vertical deflection. Baeyer also planned to determine the curvature of the seas, the Mediterranean Sea and Adriatic Sea in the south, the North Sea and the Baltic Sea in the north. In his mind, the cooperation of all the States of Central Europe could open the field to scientific research of the highest interest, research that each State, taken in isolation, was not able to undertake.^[43][51]

Significant improvements in gravity measuring instruments must be attributed to Friedrich Wilhelm Bessel. He devised a gravimeter constructed by Adolf Repsold which was first used in Switzerland by Emile Plantamour,^[52] Charles Sanders Peirce and Isaac-Charles Élisée Cellérier (1818–1889), a Genevan mathematician soon independently discovered a mathematical formula to correct systematic errors of this device which had been noticed by Plantamour and Adolphe Hirsch.^[52][53] This would allow Friedrich Robert Helmert to determine a remarkably accurate value of ⁠1/298.3⁠ for the flattening of the Earth when he proposed his reference ellipsoid.^[54]

The Siegfried Map as successor

From 1870, a map series in the 1:25,000 scale of the original Dufour Map images was published under the official name Topographic Atlas of Switzerland (German: Topographischer Atlas der Schweiz), and also known as the Siegfried Atlas or Siegfried Map (German: Siegfriedkarte; French: Carte Siegfried).