This paper addresses the question of how to represent the semantics of populations. This question is unusual in the sense that statistics is directly concerned with the definition of populations but is essentially silent on the representation of population definitions from a data modelling perspective. The motivation for this work is the development of ontologies for the representation of city indicator definitions. A city indicator measures the performance of a city in areas such as education, transportation and the environment. The definitions of city indicators rely on definitions for populations of people, built form, events, activities, and sensor measurements. This paper provides a model for representing membership extent, temporal extent, spatial extent, and measurement of populations. It demonstrates the approach by representing the definitions of city indicators as defined by ISO 37120, the interpretation of these definitions by cities, and their comparison to ascertain whether a city’s interpretation is consistent with the standard.