U.S. Railroad Network Map, 1870-1890: America, A Concise History, 3rd Edition
One feature of scalable networks: at a certain point they achieve critical mass and then scale with explosive speed. From 1861-1890 the U.S. railroad network experienced such an explosion, as illustrated in part on this map of track growth from 1870 to 1890, printed in a standard U.S. history textbook. Around 1860, the U.S. had 30,600 miles of track. By 1890 the number was 163,000 miles.