It is not easy to find maps with lines sufficiently heavy to permit of the great photographic reduction usually necessary in making illustrations from pin maps or other map representations. Quite often it is necessary for the person making a map chart to go over by hand all outlines such as borders and the divisions between States, counties, etc., to make those particular lines very much heavier than on any map which can be purchased.

A reducing glass which makes everything seen through it appear smaller is almost essential when many maps or charts must be reproduced. A convenient size of reducing glass has a single lens, about 1^ inches in diameter, and causes objects to appear from one-half to one-quarter the size of the original. The amount of reduction can be varied by holding the glass at different distances from the original drawing. In order to tell how much reduction in size is made by the glass at any given distance, it is possible to look at the original object with one eye and through the reducing glass with the other eye so that by superimposing the two images their length may be compared. When a chart has ruled lines, as co-ordinate lines, it is a simple matter to superimpose the images from the two eyes so that one square of the original equals two, three, or four squares of the image seen through the reducing glass. When the two images are thus superimposed, study can be made of the thickness of lines or other details in the reduced