In this paper we review location models, specifically covering location models, which are applicable to modeling the location of base stations for cellular phone users. The definition of cover is revisited, suggesting three new definitions of cover: two gradual cover models, and one sum cover model. A new objective for covering models, the variable radius model, is proposed. The probability that a connection can be made between the cellular phone and a base station at a given distance is defined. The objective is to minimize the probability that users cannot be serviced by at least one base station. These four new approaches are reviewed and once the research is completed four papers will be published in peer reviewed journals.