August Heinrich Petermann - Mapping The Unknown

Mapping The Unknown

Though Petermanns name appears on hundreds of maps, Wagner suggests he stopped drafting maps himself after 1862. The report concerning the Nordenskiöld voyage to the Lena, and the maps of the United States and Australia, suggest this may not be true. Perhaps he no longer designed, constructed and drafted the maps, as he had with the Barth maps, but he most likely continued to play a role in the conception and design of the maps, especially those in his fields of interest.

Petermann was very well aware that even topographic maps were not yet a true representation of reality (this is illustrated by the depiction of the Liparian Isles, which were not securely situated until Darondeau’s French survey in 1858), let alone medium- and small-scale maps of the interior of continents and the polar regions. One could still hardly speak of dense topographic, orographic and hydrological information. Though the maps in the Stieler looked dense with information they were mainly filled out with information where space in the image allowed, and the cartographers had little choice what to depict by the lack of known phenomena. The density of information did not indicate how thoroughly an area had been explored, for the cartographers selected their data and drafted the maps in such a way as to give a balanced image as possible. As Petermann put it in 1866:

“In fact, our cartographic knowledge of the territories of the earth is far less than is generally supposed. … even the African and Australian terrae incognitae shrink more and more, and there remain a few blank spots, maybe 'wild territories', where there is 'nothing'. In reality everything we see on our maps is just the first step, the beginning of a more accurate knowledge of the earth’s surface.”

Only in the detailed maps in PGM, where lots of spaces were left blank, could one really judge how haphazard and incomplete the geographic knowledge was. J.G. Bartholomew in 1902 phrased Petermann's drive as: "The filling up of the blank spaces of the unknown in his maps had such a fascination for him that rest seemed impossible to him while any country remained unexplored".

The results of the exploratory expeditions cried out for presentation in map form, and PGM published exploration results as quickly and accurately as possible. Petermann had all results he received from explorers checked against the considerable information and maps available in the Perthes Institute. This fund of knowledge grew to be so large that the Institute soon had a large library of manuscripts, books, atlases, and maps at its disposal that could vie with any university or society collection. In the 1980s it was thought that the Perthes-archives contained 180,000 printed maps and around 2,800 atlases. In the 1990s the estimate was 1,000 m of archive, some 400,000 maps (including manuscripts), and some 120,000 geographical works. All collections (currently estimated at 185,000 sheets of maps, 120,000 geographical works, and 800 m of archives) were acquired in 2003 by the Free State of Thüringen and deposited with the library of the University of Erfurht in its research center in Gotha.

But the maps went beyond a simple presentation of the itinerary by also describing the area explored with all knowledge available and pointing out gaps that remained to be filled in the current knowledge. So the impact was reciprocal. Moreover Petermann gave directions to explorers in exchange for which he was allowed to publish their results as soon as possible.