Final answer:
A choropleth map is used to show population distribution in the United States.
Step-by-step explanation:
The type of map that has been used to show population distribution in the United States is a choropleth map.
A choropleth map uses different shades or colors to represent the population density or the number of people in different areas. Darker shades or colors typically represent higher population densities, while lighter shades or colors represent lower densities.
Choropleth maps are useful for visualizing and understanding the distribution of population across regions, states, or countries.