ABSTRACT
From a software point of view, a GIS could be defined as the marriage of a graphic (or geographic) database (a GDB) with other databases-most frequently a relational database (RDB). These other databases-which contain attribute data about features in the GDB-are usually textual in nature, but sometimes consist of drawings, images or even sounds. (For example, you could key in, or click on, a street address to your GIS and be shown a photo of the house there.) The combination of a GDB and RDB allows the user to make textual queries and get graphical responses (e.g., show with a red “X” those streetlights which have not been serviced since August 1995) or, conversely, make a graphical query and get a response in text (e.g., indi cate the daily yield from
parking meters in this area that I have outlined on this image of the city using a mouse pointer).
