Putting objects of different classifications into the same scale for the sake of comparison is a relatively recent idea in the history of printing. It really wasn't until Etienne Durand's architectural textbooks of the 1850's that buildings by different architects were displayed on the same scale on the same page. Likewise, too, the cartographic depiction of mountain heights and islands and lakes and rivers side-by-side and on the same scale didn't take place in earnest until mid-19th century.
My favorites relating to geographical items are those that take, say, all of the major islands in the world and remove them to a single sheet of paper, all in scale, so that it would be easier to compare their sizes without the distraction of the rest of the map.
Here's another, just recently found in the warehouse:
This map, "Relative Sizes of the United States and the European Powers" was published by the People's Handy Atlas of the World in ca. 1920, appearing in print just a couple of years after the map of Europe was changed by WWI. (As a matter of fact this map very liberally used and without credit an earlier version published by the Geo. F. Cram company in their war atlas of 1914; it again appeared in the European War Book (by Canfield, published in 1917), calling on the information in this version and adding color. The People's History also published a 1913 version of this map though I cannot find an example of it.) Here's the map in full:
It really does put things into perspective, giving the reader a good, strong look at just how small some of these countries were in comparison with the United States. Many of the combatants of WWI are here--and its quite sobbering to think of the enormous casualties incurred in some countries and the very small area that those millions of dead and wounded would have taken if placed in a similar locale in the U.S. An excellent example of this is Belgium, fitting very nicely into less than a tenth of the state California, where so much killing and suffering occurred. Thinking of France as battlefield that was limited to about 60% of the size of the combined four states of New Mexico, Arizon, Utah and Colorado, and then thinking of most of the largest battles of WWI taking place in an area about a quarter of that is, well, incredible. Using this as a guide, less han half the state of Colorado would've been the seat of the battles of Verdun (976,000 casualties), Marne (750,000), Somme (1.2 million), Cambrai (700,000) Arras (278,000), the Spring Offensive (1.5 million) and the Hundred Days Offensive (1.8 million),plus all of the rest of the action, and you get a little bit of a better idea of the bloodiness of that acreage.
Placing things in comparison in the same scale, side-by-side, is an excellent means of insight.
Casualties in World War One (taken with thanks from the site First World War