Question

The image shows two side-by-side maps: one representing city population data from 1820 and one representing city population data from 1860. Information on the 1820 map shows the states east of the Mississippi River-excluding Florida and including Louisiana and Illinois-highlighted in yellow. This map shows approximately 12 cities in the Northern states (north of Virginia) with a population of between 10,000 and 250,000. It also shows 3 cities in the southern portion of the U.S. (in Virginia, South Carolina, and Louisiana) with populations between 10,000 and 250,000. Information on the 1820 map shows all the states of the 1820 map highlighted in yellow plus Florida, Arkansas, Missouri, Iowa, Minnesota, Wisconsin, Michigan, California, Oregon, and Texas. This map shows approximately 62 cities with a population of between 10,000 and 250,000 in the Northeastern and Midwest sections of the U.S. (north of Virginia and Kentucky). There are two cities in these regions with populations between 250,000 and 1 million. California has two cities with populations between 10,000 and 250,000. The Southern region (South of and including Virginia) has of the U.S. has approximately 10 cities with populations between 10,000 and 250,000.
Review the maps above. Based on the maps and your knowledge, what is one likely explanation for the change in the population distribution of the U.S. between 1820 and 1860?

People moved from overcrowded cities to farms in the Midwest.
Many people moved from rural farms to cities in the Northeast.
People moved from large cities in the East to settle in the Western Territories.
Many people moved from large cities in the North to small towns in the South.

Answer 1

People moved from large cities in the East to settle in the Western Territories.--new transportation and territories open up with cheap land drew people west. 

Western migration eased the crowding of Northeastern cities and provided a group of people to farm and provide food for the growing industrial centers through the North and Midwest. Railroad transportation allowed for easier travel to the West as well as roads and canals.