This is a peel coat or strip mask layer for a London drawing sheet from the mid-80s used in the production of a coloured map. The material consists of a ruby red layer bonded to a clear sheet of plastic. Placed in registration over map detail the layer is cut and peeled away for a particular colour – in this case the blue infill of the River Thames. A drawing sheet could have up to 6 of these peel coats to colour map features, from motorways to built-up areas. Subsequent revision changes to the sheet can be seen where darker red tape has been laid down and the infill recut.