LAYER MAPS Carl Ritter, in 18°6, employed graduated tints, decreasing in depth, from the lowlands to the highlands; while Gen. F. von Hauslab, director of the Austrian Surveys, in 1842, advised that the darkest tints should be allotted to the highlands, so as not to obscure details in the densely peopled plains. C. von Sonklar, in his map of the Hohe Tauern coloured plains and valleys green; mountain slopes in five shades of brown; glaciers blue or white. E. G. Ravenstein's map of Ben Nevis (1887) first employed the spectrum colours, viz., green to brown, in ascending order for the land : blue, indigo and violet for the sea. On the international map of the world, on a scale of 1 :i,000,000, which has been undertaken by the leading governments of the world, the ground is shown by contours at intervals of mom., the strata are in graded tints, viz., blue for the sea, green for lowlands up to 3oom., yel low between 30o and 5oom., brown up to 2,000m., and reddish tints beyond that height.
Until the 20th century the declivities of the ground were indi cated in most topographical maps by a system of strokes or hachures, first devised by L. Chr. Muller (Plan and Kartenzeich nen, 1788) and J. G. Lehmann, who directed a survey of Saxony, 1780-1806, and published his Theorie der Bergzeichnung in By this method the slopes are indicated by strokes or hachures crossing the contour lines at right angles, in the direction of flowing water, and varying in thickness according to the degree of de clivity they represent. Typical modern topographical maps, on scales from 1 :25,000 to i :250,00o, have, generally, contours closely spaced, printed in colours. Hachures may occasionally be found combined with contours, as in the maps of Italy on the i : ioo,000 scale.
As to the interval at which the contours should be spaced, a good rule in normal, not mountainous, country is to space them at 5oft. for a scale of sin. to the mile, and for other scales in
proportion. Thus, on a sin. map the contours would be at iooft. intervals and so on.
The United States Geographic Board acts upon rules practically identical with those indicated, and compiles official lists of place names, the use of which is binding upon Government departments.