What is the best purpose of using a historical map?

Using a historical map to observe population change over time serves an essential function in understanding how demographics can shift due to various factors such as migration, conflict, economic opportunity, or environmental changes. Historical maps provide context by allowing researchers and students to compare population distributions at different points in history, uncover trends, and analyze the implications of those changes.

For instance, a historical map can highlight how cities have expanded or contracted, indicating social and economic pressures. By analyzing the spatial distribution of populations, pattern changes over time can be recognized, which can enrich the understanding of the historical context behind these shifts, such as urbanization or rural depopulation.

While the other options are indeed valid uses of historical maps, they do not directly relate to observing population change over time in the same way. Political boundaries show governance and jurisdiction, economic systems reflect trade and resource allocation, and geographical features provide a physical context. However, only observing population changes directly reveals insights into human behavior and societal evolution, making it the best purpose in this context.