Maxwell works for the U. S. Census Bureau to keep track of urban masses in the United States. He uses to divide the country into cities of at least 50,000 people and the urbanized areas linked to them. 1. concentric zoning 2. metropolitan statistical areas 3. zone operationalization 4. city population graphs

The correct answer is 2. Maxwell works for the U.S. Census Bureau to keep track of urban masses in the United States. He uses metropolitan statistical areas to divide the country into cities of at least 50,000 people and the urbanized areas linked to them.

Explanation:

Metropolitan areas in the United States that are grouped together for statistical purposes are called Metropolitan Statistical Areas (MSA).

Unlike municipalities, counties or states, a metropolitan statistical area has no administrative function. It exists only for the socio-demographic characterization of the population living in it. A county only ever belongs to a complete territorial unit of an MSA.  

The areas mostly have a polar structure with a metropolis as their center, but do not have to contain a recognizable center. The United States Census Bureau is responsible for data collection and statistics.