Which type of datum is described as actual or assumed?

In surveying and geodesy, a datum serves as a reference point or surface for measurements. The description of a datum as "actual or assumed" relates to the concept that datums can either be based on actual measurements (physical reference marks) or on assumed values (theoretical models used for calculations).

By choosing the option that indicates "Two types of Datum," it captures the idea that there are multiple categories of datums: one that may be anchored in actual physical locations and data, such as a permanent datum, and another that represents a hypothetical or assumed framework on which further calculations can be made.

Understanding that datums can vary in their nature allows surveyors to select the most appropriate type depending on their specific project needs or the accuracy required. This principle is crucial in ensuring that measurements and outputs are based on reliable and meaningful reference points, which is fundamental in earthworks and surveying practices.