The hierarchical listing of settlements by size is known as the

The answer is:

              Rank-size rule

Explanation:

Rank-size rule is a commonly observed statistical relationship between the population sizes and population ranks of a nation’s cities.

According to the rank-size rule, there should be a larger number of small cities than bigger cities. Also, this rule predicts that the larger a city’s population is then the fewer number of cities there should be in the surrounding area with a similar population.

the difference is that white collar worker performs skills like worker as a scientist or well blue collars do physical work and they do services like being a cook.