How to Date a Road Map
Figuring out when a road map was printed can sometimes involve a bit of detective work because the year of publication may not be shown on the cover or in the legend. The table below shows the codes for the two main map producers, Rand McNally and H.M. Gousha. These codes are often found in the lower margin, printed in small type. Rand McNally first used date codes in 1919, and Gousha started in 1927. Census data and status of road construction are other clues you can use to confirm dates.
Rand McNally & H.M. Gousha Map Codes
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How to Date a Road Map: Charlie Neuschafer