Mapping the Population of U.S. Cities in 1840 – and the Philadelphia Problem

I am currently working on a large set of GeoCurrents maps that will depict the current and historical demographic patterns of U.S. cities and metropolitan areas. Several problems, however, have arisen in data selection and visualization. Most troublesome is the gradual amalgamation of separate municipalities into single cities.

Consider, for example, a map showing the locations and populations of the six largest U.S. cities in 1840 (below). It might be surprising that Philadelphia, considering its historical importance, appears as only the fourth largest, surpassed in population by Baltimore and New Orleans. But this depiction is misleading.  As it turns out, 5 of the 37 American cities with more than 10,000 inhabitants in 1840 are now mere neighborhoods of Philadelphia. New York City, as it is currently conceptualized and legally defined, was also larger than it appears on the map.  In 1840, it did not include Brooklyn, which was then the country’s seventh largest city. Boston was larger as well, as it did not then include Charlestown (see the table below).

To address this problem, I have revised the map by amalgamating what were then separate municipalities with the nearby cities that later annexed them. I did so, however, only for cities with more than 10,000 inhabitants. If smaller cities were subjected to the same treatment, the map might have to be revised again. But regardless of such difficulties, it can be clearly seen that Philadelphia was the country’s second city in 1840, with a population more than twice that of Baltimore.

The final map includes all cities (that currently exist as cities) that had more than 10,000 inhabitants in 1840. As can be seen, almost all were linked to transportation networks, serving as ports on seacoasts, estuaries, or rivers. Several are located on the Erie Canal (shown as a dotted blue line), again illustrating the importance of waterways in the pre-railroad era, which quickly coming to an end. Lowell, in northeastern Massachusetts (mapped in a light shade of red), is an interesting exception, as it emerged as a planned industrial city focused on textiles. Located on the rapids of the Merrimack River, which provided power, Lowell is often regarded as the “cradle of the American industrial revolution.”