Philadelphia was the most important center for map publishing in the early United States. Matthew Carey published the first atlas showing the newly independent country in detail there in 1795. And in the early nineteenth century, a number of Philadelphia publishers began to specialize in reference maps and atlases, geographical textbooks and primers, guidemaps for migrants and travelers, and political maps. Perhaps the most highly regarded of these early American cartographers was Henry S. Tanner. Tanner began his career as a map engraver, a craftsman who engraved copper plates with map images (usually drawn by someone else) for printing. He was a talented geographer as well, and soon began compiling his own maps. His first atlas, the New American Atlas, published from 1819 to 1839, featured the most comprehensive and up-to-date maps of American states yet published, and received great critical acclaim. However, at $30, it was too expensive for most Americans, so in 1833 he began publishing a smaller atlas, which became the New Universal Atlas. By the early 1840s Tanner had moved to New York, but his atlas continued to be published in Philadelphia, first by the firm of Carey & Hart, then by Samuel Augustus Mitchell, until 1859.

Our core map, Tanner's map of North America, comes from the 1845 edition of the New Universal Atlas, although the careful reader will note that the copyright statement at the bottom of the map ("Entered according to the act of Congress...) bears the date 1836. It was not unusual—and still isn't—for maps to be published for a period of many years or even decades without being revised. Close examination of the map will show that the longitudes on the map have been calculated from Washington D.C. The location of the Royal Observatory in Greenwich, England was not adopted as the universal prime meridian until 1884. Until that time, most American cartographers used Washington, D.C., as the prime meridian.

Tanner's map shows our continent at a pivotal moment in its political history. Its outline of North America is essentially that which we know today, with the exception of its delineation of the Arctic islands north of the Canadian mainland that were still not well known. The boundaries and the names of the countries, however, look strange to us. Colored pink and dominating the northern half of the continent is the "British Territory" that would become the Dominion of Canada in 1867. To its west, the territory we know as Alaska was still "Russian America." South of these colonial territories, the rest of the continent was composed, for the most part, of newly independent countries. The United States (in green) was not yet 70 years old, and, to modern eyes, very oddly shaped indeed. The map, shows, for example, the American claim to all of the Oregon country, including the lands north of the 46th parallel that was be conceded to Great Britain in 1846 (see Map 5). South of Oregon is a massive Mexico, nearly as large as the United States, including all of what is now California, Nevada, Utah, Arizona, and part of New Mexico and Colorado. Sandwiched between Mexico and the United States is the briefly independent Republic of Texas, founded in 1836. Its annexation to the United States in 1845 (which is not acknowledged on our map) was one of the principal causes of the U.S.-Mexican War of 1846-48. That conflict, which ended when the United States occupied Mexico City, is celebrated in the United States as the ultimate realization of its "manifest destiny" to become a transcontinental nation dominating the heart of North America. The terms of the Treaty of Guadalupe-Hidalgo (February 2, 1848) that ended the war were, however, disastrous for the young United States of Mexico. Mexico was forced to cede nearly half of its territory in exchange for $15 million, and access to the great mineral and agricultural potential of the "Mexican Cession." The history of North America would be very different indeed if the war had never occured or if it ended in a Mexican victory.

By 1848, the political map of North America would look very much as it does today. The discovery of gold in California that same year would bring about the famous Gold Rush of 1849, hastening American settlement of the new lands in the West. The new lands also placed unprecedented demands on the American government. In the 1850s American politicians insisted that transcontinental railroads were planned to help bring the West Coast settlements closer to the East. But where should they be built, and how would they be financed? North and South would bicker, then fight over the status of the new territories. Would they be free or slave-holding states? And how should the government deal with the many Indian nations and the Hispanic communities brought—however unwillingly—under the titular control of the United States? The struggle over the answers to these questions would dominate the history and geography of the country for the rest of the nineteenth century.