REFORMATION OF CARTOGRAPHY IN FRANCE 139 



comparison of barometric readings.^ Spot heights were fre- 

 quently used before the end of the eighteenth century, e.g. 

 on Mayer's 'Atlas de la Suisse', 1796-1802. 



One of the earliest examples of the use of contours for a 

 considerable area was Dupain-Triel's map, *La France con- 

 sideree dans les differentes hauteurs de ses plaines'. This pur- 

 ports to show France contoured at intervals of ten toises (about 

 sixty feet), but the representation is largely influenced by his 

 ideas on the orderly relations of mountains and plains. No 

 general levelling had been carried out at this date, so that his 

 contours were largely theoretical, but a number of summit 

 heights are given, some of considerable accuracy, especially 

 that of Mt. Blanc, and he added a vertical section across 

 France. Dupain-Triel elaborated his methods and advocated 

 their adoption in education in his 'Methodes nouvelles de 

 nivellement', 1802. Thus by the beginning of the nineteenth 

 century the method was becoming known, and with the 

 initiation of the great national surveys in the following decades 

 it passed into general use. 



A further step, the colouring of areas between successive 

 contours by a given scale of tints, was taken in Stieler's 

 'Handatlas' of 1820. This hypsometric layering allows a 

 general idea of the relief of a wide area to be formed rapidly. 

 The value of contouring lies in the fact that, unlike hachuring, 

 it enables the altitude of a particular point to be determined 

 with considerable accuracy, for heights between contours can 

 be estimated with practice. It does not, however, always permit 

 an idea of the relief to be formed rapidly, and minor topographi- 

 cal features between contours are unrecorded. Consequently 

 it is frequently combined with hachuring or hill-shading. In 

 1931, contours, hachuring, and layer colouring were all 

 employed by the Ordnance Survey in the Fifth (Physical 

 relief) edition of the One Inch map. 



^Campbell, Eila M., 'An English philosophico-chorographical chart.* 

 Imago Mundi, 6, 1949, 79.) 



