Geographic Information Systems: An Introduction, 3rd Edition

13.6 Editing and Correcting Attribute Data

Like digital map data, attribute data must be edited and corrected. These operations include error correction, updating, and amending. The editing tasks may be carried out by using standard editing tools, such as those available in word processing, or specific GIS commands. Some GISs use SQL (Structured Query Language) to manipulate attribute data in relational databases. Specific GIS commands include commands for changing object thematic codes and switching codes between objects, as well as for editing thematic codes containing texts.

The guidelines for entering data may change with time, mandating changes in the codes of older data. Usually, common mathematical signs such as +, −, *, and / are used for this purpose. The currencies in which prices in attributes are expressed may be changed [e.g., from U.S. dollars ($) to pounds sterling (£)] by entering an exchange rate. Relational and other databases used to store attribute data usually incorporate effective editing tools. These permit a variety of operations, including searching for members of a prescribed class and then editing one by one, or assigning new values to an entire class using a single command.

Incorrect attribute values are often very difficult to detect, both in raster and in vector data. In raster data attributes are an integrated part of the geometry, and erroneous single values can be relatively easy to spot visually. In many raster GISs one can also use a run-length ...