Collections of Voyages. Surveys. Classes of Maps.
The 18th century saw great progress in the collection and arrangement of geographical material, and in the work of surveying and map-making. Collections of voyages and travels were brought together in the four quarto volumes of Astley (1745) and the two folios of Harris (1764); while Dr Hawkesworth edited the Government voyages to the Pacific in 1773. Sir Joseph Banks was the great patron of geography in England, aided by the indefatigable labours of such critical geographers as Rennell, Dalrymple, and Barrington; while in France the great cartographer DAnville introduced a habit of critical accuracy, and caused a complete revolution in the art of map-making.
Towards the close of the century it was recognized that geography served more extensive and important uses than had ever before been supported. The route survey was sufficient for the traveler or soldier, while accurate charts guided the mariner across the ocean. But surveys are also the basis of statistics and of administration, and rigorous accuracy became necessary. Surveys on a trigonometrical basis, which have been proceeding in all the countries in Europe (except Turkey) and in India during the present, were commenced in the last century. In Great Britain the Ordnance Survey was begun in April 1784, when General Roy measured a base line on Hounslow Heath. The triangulation of the British Isles was commenced in 1784 and completed in 1852. Maps based on trigonometrical surveys may eventually explain and illustrate the physical aspect of the whole globe, but at present they are necessarily confined to those nations which are in the front rank of civilization.
Countries which are not so advanced are still obliged to be content with such maps as sufficed for all the world in the last century, before the results of trigonometrical surveys were available. These secondary maps are adapted for the requirements of the countries which use them, being based on positions fixed by astronomical observations, on cross bearings, and observations, on cross bearings, and often on chained distances.
The third class of maps includes the work of explorers of unknown or little known regions, and of geographers who delineate the features of such regions by compilation and by intelligent collation of the work of travelers.
There are thus three grand divisions in the character and uses of maps. There are first those which aim to minute accuracy, and which are intended as documents for administrative purposes, and in pursuing exact statistical investigations. Secondly, there are maps which are based on less accurate surveys of countries less populous or less advanced in civilization; these are useful for political, geographical, and military purposes, but are not to be relied on to the same extent or in the same way as is the case with those based on trigonometrical surveys. Thirdly, there are the rough compiled maps of little known regions, which are constantly in course of improvement, and which do the work of pioneers.
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Geography - Table of Contents