An imaginary field placed around certain positions on a graphical display to aid user input. For example, when inputting a line drawing, existing end points of lines may have gravity fields associated with them that attract the locator input device. As the device approaches the point it will therefore snap onto the point with the gravity field. A gravity field greatly assists the input of a connected set of lines for the operator, who only needs to get close to the desired position rather than identifying it precisely.