Databases are computer systems designed to store information in a systematic way so that their contents can be easily accessed, managed, changed, and augmented. Spatial databases are such systems designed specifically to include data with spatial attributes, such as geographical location, distance, and extent. The software used to manage and query a database is known as a database management system (DBMS). The most prevalent type of database is the relational database, a tabular scheme in which data are defined in terms of simple data types and operations so that it can be reorganized and accessed in a number of different ways. Most spatial DBMSs extend the relational model to include more-complex spatial data-types and operations. All geographic information systems (GISs) use a spatial database with, in addition, functions for presentation, visualization, and analysis of the spatially referenced data.