256 National Geographic Magazine. 
in bold relief. In other words the map is a diagram rather than 
a picture. 
In the representation of relief on the one inch series, two sys- 
tems are common, contours and hachures. Contours represent 
the successive shore lines which water at rest would form 
in following the modelling of the ground at successive stages 
or elevations. If now we assume that the water, having reached 
the highest point, is allowed to retreat steadily to sea level the 
paths which the particles of water would take from all points of 
the surface are those which the engraver would endeavor to re- 
produce in the shade lines of a hachured map. In addition he 
would adopt an arbitrary scale of shade increasing with the steep- 
ness of the slopes, from white on a horizontal surface to dead 
black on slopes of forty-five degrees, or greater, to produce the 
effect of a model of the surface illuminated from above. 
In the Irish maps this effect is bolder and more artistic, an 
illumination from the northeast quarter having been carried out. 
The shade lines still preserve the paths of particles of water in 
motion on the surface, the color values being deeper on the 
eastern and southern slopes, shadows have even been projected 
across valleys and horizontal surfaces are in half tone, producing 
much the same effect as the illumination of the country at sunset 
in midsummer. ¥. 
The Irish maps exhibited are considered the finest specimens of 
careful hill shading and will bear critical examination. For com- 
parison with these, other topographic maps are exhibited of 
many scales and countries. 
So far attention has simply been drawn to a few of the problems 
of map-making, which are, briefly : "2 
Ist. The reproduction on a finite scale on a plain surface, 
of the natural features of the terrain, with all the artificial boun- 
daries and objects added by man, so far as the scale permits. 
2d. The extension of such a series of maps to cover a large 
area of country still carried out with as little distortion as pos- 
sible. 
3d. The reproduction of such maps on suitable scales to meet 
all demands. 
If the conception is still carried out that the map, at a distance 
of two feet, is but the image of the ground viewed from above, 
then the cadastral map of England, from which areas of fields 
and estates are measured for valuation purposes, would represent 
