There is often an analytical need to combine maps digitized from separately compiled map sheets into a sheetless product. If the maps are strictly compatible, the borders will overlay exactly and features will cross the borders smoothly. Digitized products, particularly those entered manually, fall short of this goal. Due to imperfect geodetic references and other flaws of compilation, many existing maps fail to match their neighbors exactly. These circumstances call for a process we call “zipping”—the ability to merge map sheets so that edges disappear and features cross the boundary smoothly. Advanced overlay software that provides a fuzzy tolerance to remove slivers can be used to perform this process, but the results are not fully satisfactory. This paper introduces an algorithm call Zipper that limits its calculations to the edges of the maps instead of invoking a general-purpose processor. It creates a clean topographical product with minimal manual intervention. This public-domain processor has bee...