The type of sampling used is cluster.
Explanation:
The process that is used to study the characteristics of a larger population by observing only a smaller group of larger one is called sampling. There are two important terms used in this process. One is larger population and the other one is the sample size. The type of sampling method that we use in a sampling process is determined by the type of analysis that we use.
The process in which the larger population is divided into smaller groups mainly based on the geographic features is called as cluster sampling. The groups in which the larger population is divided is called groups or blocks. The random selection is applied for selecting the groups.