Image courtesy of the U.S. Census Bureau
One of the most common statistics used to describe a country is “density.” But what does this mean and is it really a good measure of population or any other characteristic of a place?
Assuming we are talking about population, density can be defined as the average number of people per square mile (or square kilometer). And this is the problem – it is an average that assumes people are evenly spread throughout the area being considered.
The population density of the United States is about 87 people per square mile (about 34 people per square kilometer), but reference to the 2000 Nighttime Map of the U.S. makes clear that the U.S. population is not evenly spread across the country. This map shows distribution, which can be defined as the actual arrangement or spread of people within a given area.
Testing the Definitions
a) Distribute the handout of population density by state (PDF). At the state level, the map shows a better picture of population distribution within the U.S., but there are still some obvious problems.
b) Have students locate your state. According to the handout, what is the population density in your state? Do the students think that the state’s population is evenly distributed throughout the state, as the map suggests?
c) View the U.S. Census Bureau’s "Gateway to Census 2000"
i. Use the drop-down menu under Data Highlights to select your state. Click “Go,” then select the “State by County” table for “Population, Housing Units, Area, and Density.”
ii. Next, download a state/county outline map for your state.
iii. Distribute maps and data and have students use the data in the column “Density per square mile of land area: Population” to construct a choropleth map of population density by county for your state.
Note: A choropleth map uses decreasing shades of color to show decreasing numerical values. See the map on the handout for an example.
d. Lead students in a discussion of density and distribution as they relate to the maps they have made. Is density a good measure of population?
Extending the Activity
Encourage students to discuss what factors may influence the distribution of population within your state.
Ask students if they think the population within your county is evenly distributed, as their maps suggest? How can they test this?
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