Geographic Information Systems: An Introduction, 3rd Edition

6.8 Discrete Georeferencing Systems

In discrete georeferencing systems the positions of phenomena are refferenced relative to fixed, limited units of the surface of the Earth. Objects are linked to geography using the reference units as tags; this is known as the tagging method or georeferencing by geographic identifiers. With this type of system, we know that each object is located within and linked to the specified reference unit, but the location within the reference is unknown. Typical area reference units include:

• Address and street codes
• Postal codes and area name
• Property units
• Administrative zones and statistical units
• Regular grids and map sheets

The unit size determines the accuracy of registration: The smaller the units, the greater the accuracy. It is assumed that, in principle, the units are given a standard specification. In practice, however, the division between units can be relatively diffuse (e.g., it can be difficult to define exactly which geographical area is covered by an area name).

Many geographical phenomena are registered in discrete systems. Address and street codes, for example, may be used to indicate locations along roads (Figure 6.16). Reference to a whole street gives a clear discrete georeference. Roads and streets are often divided into selected registration units, such as city blocks, or fixed or variable distances. In addition, each house has its own number. As a road is gradually split up, georeferencing becomes almost continuous, although ...