Continuous raster layers are quantitative (measuring a characteristic) and have related, continuous values. Continuous raster layers can be multiband (for example, Landsat TM) or single band (for example, SPOT panchromatic).
Satellite images, aerial photographs, elevation data, scanned maps, and other continuous raster layers can be incorporated into a database and provide a wealth of information that is not available in thematic layers or vector layers. In fact, these layers often form the foundation of the database. Extremely accurate base maps can be created from rectified satellite images or aerial photographs. Then, all other layers that are added to the database can be registered to this base map.
Once used only for image processing, continuous data are now being incorporated into GIS databases and used in combination with thematic data to influence processing algorithms or as backdrop imagery on which to display the results of analyses. Current satellite data and aerial photographs are also effective in updating outdated vector data. The vectors can be overlaid on the raster backdrop and updated dynamically to reflect new or changed features, such as roads, utility lines, or land use. This chapter explores the many uses of continuous data in a GIS.
See Raster Data for more information on continuous data.