Geographic Information Systems: An Introduction, 3rd Edition

12.1 Database

Within the framework of GIS, data are divided logically into two categories: geometrical data and attribute data. This division may extend to a similar division of physical storage, although the relationships between the two categories of data must be preserved regardless of whether the division is logical or physical. In current GIS, this condition is satisfied through one of five approaches to the overall database storage involved:

1. Geometrical data and attributes stored in the same file/database
2. Two separate database systems, one for geometrical data and one for attribute data in a relational database
3. A single relational database that stores both geometrical data and attribute data
4. One database for geometrical data connected to several different databases for attribute data
5. Several databases for geometrical data and attributes joined into one system—a distributed database solution

GISs that have geometry and attributes stored in the same file also have a tailor-made file-based management system (Figure 12.1). The advantage of this solution is that rapid search is usually included in the data structure. A series of operations and analyses can be performed on both geometry and attributes. The link between geometry and attributes is very close and special for each system. To increase the search and record speed, data are split into different layers and area units. Map sheets are often used as a storage unit, but it will be very difficult to change the size of the ...