Which of the following defines a frontier area in terms of population density?

The correct definition of a frontier area in terms of population density characterizes regions with very low population concentrations, where communities are sparsely populated. According to historical and statistical standards used by various organizations, a frontier area is generally defined as having fewer than 10 people per square mile, indicating an extremely low density of inhabitants.

In this context, option B, which states "20 or more people per square mile," does not align with the definition of a frontier area. Areas with 20 or more people per square mile would typically indicate a higher population density than what is recognized in frontier classifications.

Understanding this helps clarify that frontier areas are often associated with rural or less-developed regions, where services and resources may be limited due to the sparse population. Therefore, the correct range for defining a frontier area would resonate more closely with the lower population thresholds outlined in the other options.