The article outlines how to use the convergence of collections to determine the position of a mobile device based on the WiFi radio signal strength with the use of fuzzy sets. The main aim is the development of the method for indoor position determination based on existing WiFi network infrastructure indoors. The approach is based on the WiFi radio infrastructure existing inside the buildings and requires operating mobile devices such as smartphones or tablets. An SQL database engine is also necessary as a widespread data interface. The SQL approach is not limited to the determination of the position but also to the creation of maps in which the system dening the position of the mobile device will operate. In addition, implementation issues are presented along with the distribution of the burden of performing calculations and the benets of such an approach for determining the location. The authors describe how to decompose the task of determining the position in a client-server architecture.