Most maps display a location at a particular time.
By comparing information from two or more points in time, a mapmaker can create a map that represents change. But maps also show those features at a given point or interval of time. Maps may depict features that remain unchanged over long periods of time, such as mountains. They may also show things that change frequently, like roads, population, or the quantity of effluent discharged at a facility. So, an accurate map also identifies the period it is portraying.