Rethinking Levels of Measurement for Cartography

Stevens' measurement levels (nominal, ordinal, interval and ratio) have become a familiar part of cartography and GIS. These levels have been accepted unquestioned from publications in social sciences dating from the 1940s and 1950s. The Stevens taxonomy has been used to prescribe appropriate symbolism (or analytical treatment) to each scale of measurement. This paper reviews the process by which these levels became a part of cartography, as well as subsequent literature that cartographers have all but ignored over the intervening four decades. The paper concludes that the four levels of measurement are not adequate to cover the circumstances of cartography, and that attribute issues alone do not provide a sufficient guide to symbolism or analytical treatment. A broader framework for measurement must be considered, including the relationships of control that constrain variation in one component to permit measurement of another. An informed use of tools does not depend on numbers alone, but on the whole "measurement framework," the system of objects, relationships and axioms implied by a given system of representation.