Page:Graphic methods for presenting facts (1914).djvu/132

 will be apparent from the similarity in the shape of the curves for the different years.

Philadelphia Commercial Museum

Fig. 101. Comparison since 1850 of the Merchant Tonnage of the United Kingdom with that of the United States. Gross Tonnage is Given for the United States and Net Tonnage for the United Kingdom

The chart is arranged backwards in that it reads from right to left. At first sight one thinks everything is growing smaller instead of larger. The different bars so closely grouped together are exceedingly difficult to interpret. See Fig. 102

In order to use a fairly large vertical scale so as to make the fluctuations stand out clearly, it was necessary to avoid entirely the zero lines for the curves plotted in Fig. 103. The omission of the zero lines may cause the fluctuations from month to month to appear greater than their true size would warrant. It is sometimes possible to plot a chart on the general scheme of Fig. 103 so as to use zero lines, but many times it will be found that the zero lines cannot be used without adding confusion. Though it would be preferable to have the zero lines included, the gain due to the arrangement of the curves as shown here for comparative purposes is great enough to offset the disadvantage of not having the zero lines on the chart.

The zinc plate for Fig. 103 was prepared directly from typewritten copy, with no handwork involved except to make heavier some of the green background lines and to draw the actual curves themselves. Notice in Fig. 103 that the month at the left of the chart is December, and that the point plotted in each case for December at the left is exactly the same as the point plotted for the December shown at the right of the preceding curve. By repeating the last month of each curve in this manner, the interpretation of the curves is much simplified so that the reader can see at once what has been the tendency of the curve from December to January each year. If the December