Change can also be detected by combining maps and images. GIS overlays on image data can provide a means for better interpretation and for detection of changes, e.g. new buildings, changes in parcel boundaries or forest limits. The results can be directly combined with other data in the GIS, for example to update LULC information. The difficulties lie in reconciling the accuracy of different sources and their registration.
Past and current maps of land use/land cover can also be combined and, if necessary, integrated with topographic and geological data. In addition to difficulties arising from differences in accuracy of the sources and their registration, thematic categories in the maps may not always match.