We describe an examination of various physical and human factors which influence the effectiveness of location-based applications. By varying both the target location size and position system accuracy, and hence the ease of use of an application, we are able to identify physical constraints which apply as well as quantifying performance and evaluating human factors. A movement analysis is proposed which allows us to formulate a set of equations that relate the time to find the target to the target location size, distance and positioning system accuracy. We validate our work using a game based application, digital hopscotch, in which the location size and the accuracy of the positioning system are varied. A further set of tests is performed outdoors using a GPS-based application. We show that the results from these experiments concur with the results from our equations. This work may be usefully embedded in software packages that allow designers to build location-based applications.