Input / Output of a query

A query relates to specific datasets and the data type defines whether a certain query is possible or not. The common data types in a GIS are vector and raster and also tables. Thus, the queries on raster data are different than the queries on vector data, although the question to be answered is the same. The number of data sets included into the query also plays a role. The query can refer to a single or multiple data sets. The relationships between the data involved in the query are given via the topology (geometry) or the tables (theme). Tables can also be related to each other. The content of the tables can be linked via key attributes. Thus, a query can be performed over several linked tables.

The result of a query can be presented in different forms. The result should be presented in a form which is easy for the user to read. Normally, the results are presented as maps, tables, or figures, or in another format which allows data sharing. The following are examples of data presentation:

1. Digital data transfer
2. Interactive graphics on screen
3. Tables, reports, and similar representations
4. Passive graphics in form of maps