Page:Graphic methods for presenting facts (1914).djvu/27

 than the sector method and would, in a very short time, become so well known that it would be read much more quickly and accurately than the method involving sectors.

Adapted from Data, Chicago

Fig. 4. Utilization and Accompanying Wastes of One Year's Coal Supply for Locomotives on Railroads of the United States

The double scale permits reading this chart in tons or in dollars

In Fig. 4 a double scale is used by which the same data can be interpreted from two different standpoints. On the left the scale is given in millions of tons, and on the right in millions of dollars. The reader can interpret the chart from whichever standpoint he prefers. Though this chart is arranged vertically instead of horizontally, it really makes little difference which way the bars are placed. As a general thing, the horizontal arrangement lends itself more readily to the use of type so that the reader may read type statements without having to turn the book.

In Fig. 5 the whole population of the United States is divided first into native white, foreign white, and colored, then each of these groups is subdivided according to place of birth. This is an excellent type of chart to use if subdivisions in the component parts of any unit have to be shown. If the scale to which the chart is drawn is specified, it is possible for the reader to measure, with an ordinary ruler or with an engineer's scale, the exact percentage size of each of the different components.

If the chart is made on co-ordinate paper with ruled squares, the reader can obtain the size of each component direct from the co-ordinate lines. The trouble, however, with using co-ordinate paper for charts of this sort is that the components are likely to begin and end at points not falling upon the co-ordinate lines, thus making it necessary to count