Instances of the class Observation are used to specify observations about an entity at a particular time. The principal properties of an Observation are observationAbout, measuredProperty, statType, [[value] and observationDate and measuredProperty. Some but not all Observations represent a QuantitativeValue. Quantitative observations can be about a StatisticalVariable, which is an abstract specification about which we can make observations that are grounded at a particular location and time.

Observations can also encode a subset of simple RDF-like statements (its observationAbout, a StatisticalVariable, defining the measuredPoperty; its observationAbout property indicating the entity the statement is about, and value )

In the context of a quantitative knowledge graph, typical properties could include measuredProperty, observationAbout, observationDate, value, unitCode, unitText, measurementMethod.