1. GIS a spatial operation such as a transparency superimposed on a map or a procedure using computers that combines two or more data sets —note e.g., an overlay can be performed between management units and soil data showing how much area of each management unit lies on which soil types, or vice versa 2. a sheet material, e.g., plastic, bonded to the surface of (mainly) panel products, to provide a protective or decorative increase in strength, or a base for painting 3. one or more sheets of paper impregnated with resin and used as face material, mainly over plywood but also on lumber or other products —note overlays can be classified as masking, decorative, or structural, depending on their purposeThis definition last updated 07/22/2008