A pictorial query language for geographical databases

In this paper a Pictorial Query Language (PQL) for Geographic Information Systems (GIS) is proposed. The user queries the GIS drawing symbolic objects, combining them together and selecting the derived result among those ones proposed by the PQL. The used interface is part of the Scenario GIS developed using an object oriented environment. This PQL makes easier the formulation of a complex query and simplifies user approach to the system, maintaining a strong expressive power. An overview on the data structure type, on the operators and on the relations among geographic entities is briefly made. The Visual Algebra and the relative operators are defined. The pictorial operations associated to the above mentioned algebra are described. Finally, an example of query and its visual composition on the screen is shown.