Back to this week’s map and hints.

Answer: This week’s choropleth depicts the percentage of the population in each U.S. county that identifies as Native American. In the counties that are colored in darker red, a higher percentage of the population is Native American.

The data for this map came from the 2010 U.S. Census. As we mentioned in the introduction to this week’s map, we did not use equal ranges for the data because our goal was to highlight counties with extreme values. Here’s the scale we used: the darkest red is for counties with over 70% Native American population; the second darkest red is for counties with 50–70% Native American population; the third darkest red is for counties with 30–50% Native American population; the fourth darkest red is for counties with 20–30% Native American population; the fifth darkest red is for counties with 10–20% Native American population; the third lighest red is for counties with 5–10% Native American population; the second lightest red is for counties with 1–5% Native American population; and the lightest red is for counties with less than 1% Native American population.

The Census actually collects two different kinds of race data. Before asking a person what race he or she identifies as, the questionnaire asks whether the person considers him or herself to be of one race or multiracial. A person who selects “multiracial” may then select multiple races. Consequently, the Census gives data for those who are “one race: Native American” as well as those who are “Native American, alone or in combination with one or more other races” (to use the parlance of the Census). An interesting bonus question for this map is to try to figure out which of these two categories of data we have used. The answer appears in the final paragraph on this page.

If you took the initiative to look up individual counties that appear dark on this map, you likely discovered that many of those counties contain reservations given to particular tribes. These include the counties mentioned in Friday’s hint: Menominee County, Wisconsin; Oglala Lakota County, South Dakota; and Apache County, Arizona. All of these counties are named for the tribes that own the land that comprises them, which should have been a fairly obvious hint!

One thing to bear in mind, however, is that not all Native Americans live on reservations. People who identified in the 2010 Census as at least part Native American live in all but two of the counties of the U.S. (One of those counties is Kalawao County, Hawaii, home to a total population of only 90 people. 48.3% of the residents of Kalawao County identify as Pacific Islander, but Native Hawaiians are not categorized in the Census in the same category as Native Americans) If you submitted an answer for this week’s map that said something to the effect of, “this map shows the percentage of land in a county set aside as a Native American reservation” or &ldqou;this map shows the percentage of Native Americans who live on reservations,” we did not give you any points. There are only 326 reservations in the U.S., and not every county has one.

One of the most interesting features of this map is the dark colors in the eastern part of Oklahoma. In 1830, the U.S. Congress passed the Indian Removal Act, which authorized Andrew Jackson to move Native Americans west of the Mississippi River. Land in the present-day state of Oklahoma was designated as a homeland for the so-called “Five Civilized Tribes”—the Choctaw, Chickasaw, Cherokee, Creek, and Seminole. Members of these five tribes were forced from their homelands in the Southeastern U.S. and relocated to Oklahoma via the routes now known as the Trail of Tears. For the rest of the nineteenth century, the eastern part of Oklahoma was known as Indian Territory. In 1907, this territory joined with the neighboring Oklahoma Territory (in the western part of the state) to enter the Union as the state of Oklahoma. Oklahoma continues to have a sizeable Native American population—the enduring demographic legacy of government policies dating back nearly two centuries.

How can you tell whether this map depicts people who identify as only Native American or those who identify as Native American alone or in combination? These two sets of data would, obviously, produce similar maps. But the biggest difference is in the state of Oklahoma, which has had a large, settled Native American population for a long time. Consequently, many Native Americans in Oklahoma have intermarried with people of other races, especially white. Lots of famous Oklahomans have considered themselves to be part Native American, including Jim Thorpe, Will Rogers, and Sarah Vowell (we’ll resist the temptation to add Elizabeth Warren to this list). On a map that showed the percentage of the population that identified as Native American alone, the counties of Oklahoma would be much lighter. This map, by contrast, shows the Oklahoma counties fairly dark, so you can conclude that it is a map of those who identify as part Native American, alone or in combination with other races.