Chapter III
SIMPLE COMPARISONS INVOLVING TIME
 | An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|Graphic methods for presenting facts (1914).djvu/56}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |  |
United States Statistical Atlas, Census of 1900
Fig. 36. Foreign-born Population of the United States in 1850 Compared with that in 1900, also the Proportion of the Different Nationalities in the Two Years Compared
The method of presentation by means of a circle with sectors
is not inaccurate when only component parts are to be
shown. Here, however, we have two different circles compared
on the basis of total area. The reader cannot compare
the areas visually so as to get the correct ratio measure
of the increase in total number of foreign-born population.
Horizontal bars are much preferable to circles when
comparisons are to be made
Though in making comparisons, the horizontal bar divided into blocks is superior to the circle divided into sectors, the circle and sector arrangement is not inaccurate when only the component parts of any unit are to be shown. In the case of Fig. 36, however, the comparison is between two circles, the divisions into component sectors being only an incidental feature. In this diagram, copied direct from the Statistical Atlas of the 1900 Census, it is practically impossible to tell how much larger the foreign-born population was in 1900 than it was in 1850, for it is necessary to compare the two circles on an area basis. To the average person this is an almost impossible task, because it is not feasible to fit one circle inside of the other visually as two horizontal bars may be fitted. If the circle for 1900 were estimated as twice the diameter of the circle for 1850, it would mean that the foreign-born population in 1900 was four times as great as that in 1850. If, however, the ratio were something less simple than this, interpretation of the chart would be difficult even by the processes of mental arithmetic. If the ratio between the diameters were,
