Spatial-Query-by-Sketch is the design of a query language for geographic information systems. It allows a user to formulate a spatial query by drawing the desired configuration with a pen on a touch-sensitive computer screen and translates this sketch into a symbolic representation that can the processed against a geographic database. Since the configurations queried usually do not match exactly the sketch, it is necessary to relax the spatial constraints drawn. This paper describes the representation of a sketch and outlines the design of the constraint relaxation methods used during query processing. Traditional methods for spatial querying are tedious [17] . The difficulties of communicating a user's request to a spatial database through conventional spatial query languages becomes most apparent when several users have to work together. Fundamental to this problem is the fact that verbal descriptions of spatial situations are frequently ambiguous and may easily lead to misinterpretations, particularly in multi-language groups. The use of traditional spatial query languages has serious limitations, because geographic concepts are often vague, imprecise, little understood, or not standardized. As an example, take the notion of the spatial predicate cross whose semantics may vary depending on the context in which it is used, the meaning of the objects to which the predicate relates, and the topology and the metric of the particular configuration [39] . These drawbacks make most current spatial query languages error-prone and difficult to use. Graphical user interfaces provide only little improvement for such query languages, because they use the same type of syntax and grammar as the typed languages, and their primary advantage is that they release users from remembering the particular syntax. We attempt to overcome the limitations of conventional spatial query languages by considering alternative interaction methods between users and geographic data in a geographic information system. With the advent of pen-based user interfaces, a more intuitive style of interaction with spatial data is made possible than typing a query or composing it from menus. Pen-based user interfaces are expected to become more important in the future with an increasing demand for multi-media systems in most any application domain [31] . Particularly for the interaction with geographic data, pen-based user interfaces provide a series of advantages over current interaction
SpatialQuery-by-Sketch tries to offer an efficient visual interface for retrieving spatial objects satisfying a spatial query in geographic information systems REF .
Query Processing in Spatial-Query-by-Sketch
Journal of Visual Languages and Computing
Computer Science