1. A method implemented in a computing device, the method comprising: storing, in the computing device, an identifier of a geographical region having a predefined geographical boundary; storing, in the computing device, a set of cell identifiers, each of the cell identifiers identifying a cell that is determined to be within the predefined geographical boundary; receiving, from a mobile device, a location of the mobile device; converting, by the computing device, a set of coordinates of the location of the mobile device to a first cell identifier; determining, by the computing device, whether the location of the mobile device is within the geographical region based on searching the set of cell identifiers to determine if the set has the first cell identifier.