These eliminate the manual work of following the lines and ensure consistent, repeatable results each time a map is scanned. Although scanning is quicker than digitizing, only good quality maps can be scanned, and even then the quality of the products is generally not as high. However, as in most areas of computerization, the technology is continually being improved. The quality of input data will affect the quality of GIS products regardless of the sophistication of its hardware and software. In many cases, inventories of natural resources are often not completed or up to date and information in maps may have to be revised before digitizing.
Processing can operate on the spatial and non-spatial aspects of the data, or on both.
Typical operations include overlaying different thematic maps, computing areas and distances, acquiring statistical information about the attributes, changing the legend, scale and projection of maps, and making three-dimensional perspective view plots using elevation data, as shown in the figure at right. Data output and presentation deals with the way the information is displayed to the user. As in any map-making operation, data collection and data input operations require high standards of design and work, intensive training and frequent monitoring for quality control. In other words, in addition to having the right hardware and software to do the job, effective utilization of a GIS requires adequate staff training as well as planning, organization and supervision in order to maintain the quality of the data and the integrity of the final product. This ensures that the necessary specialized subject matter expertise is applied in the interpretation and evaluation of data.