An interactive surface for enabling user interaction with software in a computer system via a sensing device, the interactive surface comprising: visual information relating to a drawing field and the computer software; and, coded data indicative of an identity of the interface and reference points on the surface, the coded data comprising a plurality of substantially undifferentiated marks positioned relative to a predetermined pattern, each mark having a plurality of possible values; wherein, the coded data is readable by the sensing device in order to generate indicating data that is indicative of the identity of the interactive surface and movement data being indicative of the sensing device's movement relative to the interface surface; such that, the interface surface is identified by the computer system and the movement data is used to identify the drawing field; and the computer software is operated at least partly in reliance on the movement data, and in accordance with instructions associated with the drawing field.