This paper presents a new quantitative means to measure how cellular areal network coverage is distributed over a country or region, in particular the extent to which coverage is concentrated to urban regions. We present a new Cellular Coverage Inequality (CCI) index useful as a quantitative measure of fairness in a urban-rural perspective. Necessary data to determine the index are, on one hand, a geographical rurality map, essentially derived from a population map and, on the other hand, a cellular coverage map of the kind typically published by cellular operators. Our CCI-index then allows different cellular networks to be compared in terms of their coverage fairness and urban-rural inequality. Alternatively, the urban-rural coverage divide can be monitored over time. We give examples of the use of the CCI index for public coverage maps of Sweden over the years 2013-2020.