A method for providing a network service of a cellular communication network covering a geographical area for a plurality of mobile terminals, the method comprising: defining a grid covering at least a part of the geographical area with grid fields, framed by grid lines and spaced by a grid spacing; providing grid information comprising reference point information and information on said grid spacing, generating crossing information in response to one of the plurality of mobile terminals crossing one grid line, based on said grid information and on position information of the at least one mobile terminal, and keeping grid field information for at least one grid field comprising identification information of the one mobile terminal when inside the one grid field based on said crossing information.