GIS Files 2: Geographical data

2.1: Data capture from maps (1)

With so many paper maps in existence, it's not surprising that a lot of geospatial data has been created using them as a template. It is also possible to create geospatial data by taking measurements direct from physical surveys. These days, most geographical information is captured in digital form at the point of initial survey. But some data is still created by converting paper maps into electronic form. The two most important methods are scanning and digitising.

Scanning

You are probably familiar with scanning technology already – many home and office PCs come with a desktop scanner. The scanner will take any printed image and take a picture of it. By capturing the image in digital form it can be stored on the computer and displayed on screen.

Scanning a map is a straightforward process and generally fast, but it does not provide for the capture of attribute information for features, such as the address of a building. As discussed in Chapter 1, raster data uses up a lot of disk space, so rasterisation of maps by scanning is not always the most efficient method. However, it is very good for storing the cartographic style of the map.

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