Simple linear regression is a method that allows a ‘best-fit’ line to be added to a set of points on an x-y plot or scatter-graph. There are many uses for regression in geography and related disciplines. For example, when you know the value on the horizontal axis it allows you to define the most likely value on the vertical axis. Where one of the axes represents space or time the best-fit or regression line can be used, with care, to make predictions that go beyond the range of the measurements, providing a method of prediction. Relationships defined using regression can also be extended into the past allowing, for example, the reconstruction of past climate and environmental change.