Geographic Information Systems: An Introduction, 3rd Edition

12.3 Databases for Map Data, Indexing

Databases for digital map data should be able to manipulate records of varying length efficiently. For example, line length may vary considerably, resulting in a corresponding variation in the number of coordinates entered. Standard databases cope poorly with such variations, which is why many GIS suppliers have developed their own databases for digital map data. These database systems reflect geographical reality by such means as requiring that data on objects of the same type, such as the lines forming a property boundary, be stored in close proximity in the database, to speed up the response.

Tailor-made database systems using relatively simple file structures are often used for geometrical data. These databases are usually based, to a large extent, on network or relational databases or a combination thereof. To carry out analysis of the data, such as overlay, network analysis, and so forth, the data are stored in a topological structure with node tables, link tables, and polygon tables, as well as coordinate tables, as described in Section 4.2.3. As far as the geometry is concerned, the spatial search criteria also often have certain demands for special structuring (indexing) of the data. In the case of attribute data, the database system's own indexing technique is often used and can be quite efficient.

General points about indexing

A prerequisite for the efficient use of GIS is that information search is rapid. Users normally expect the ...