News cameras take an overhead picture of a part of a crowd at an outdoor event. Journalists then count the number of people in the picture and use the sample to estimate the total number of people in the crowd. This process is an example of

The journalists count everyone in one selected area of the crowd—the people visible in the overhead picture—and use that group to estimate the whole crowd. Sampling a naturally occurring group, or cluster, and observing its members is cluster sampling. The description does not say the people were chosen individually at random or divided into strata.

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