Phenomena: a visual query language for continuous fields

In the present paper we introduce a visual query language, Phenomena, able to manage continuous fields, which represent real-world events. In GIS applications, continuous fields represent phenomena related to the environment and its resources. Recently, much attention has been devoted to the field view of geographic phenomena, where the geographic world can be described by a number of variables, each measurable at any point. While objects are distinguished by their dimensions, and can be associated with points, lines, or areas, fields can be distinguished by what varies, and how smoothly. Thus, when dealing with continuous fields, a basic requirement is represented by users' capability to capture some features of a scenario, by selecting an area of interest and handling the heterogeneous events involved. Phenomena makes this task easy to implement, thanks to a quite intuitive visual representation of both continuous fields and conditions, which involve them. A peculiar feature of the visual language is the use of geometries to select portions of continuous fields, on the basis of spatial conditions. The heterogeneous nature of fields and objects is also reflected in the visualization of query results.