For example, one can estimate by interpolation the population of a country at any time between known 10-year census figures. This would normally be done on a graph, the shape of the curve between known points enabling a good estimate to be made of the interpolated value.
Extrapolation involves estimating an unknown quantity that lies outside a series of known values.
Thus one could obtain a figure for the population of a country five years after its last census, by extending the population curve after the last known value. Interpolation The Bloomsbury Dictionary of English Literature 2. A Dictionary of Geography 5. All rights reserved.