3.2 Scanning maps to produce raster data Scanning is a relatively straightforward process in which paper maps are placed on a scanner and a raster copy is produced. Smaller scanners are often relatively inexpensive; however, larger ones suitable for large map sheets are still expensive. The spatial resolution of the scanner, usually expressed in dots per square inch (dpi), and its spectral resolution (the number of colours it can distinguish), must be borne in mind, as this will affect the accuracy of the resulting data. Converting from the resulting scan to the type of raster data described in the previous chapter will require a certain amount of post-processing. If the source maps are relatively simple and focused on a single theme, such as land-use or soil type, this may be quite straightforward, whereas converting from more complex sources can be very time consuming. | 
