| Sketching, and in particular freehand sketching is a very old form of communication that has been used to visualize, store, and exchange information for thousands of years. However, and despite its expressiveness it has not yet become a frequently used modality to interact with computer systems. Geographic Information Systems (GISs) have a particular need for such advanced forms of interaction, because they involve complex and heterogeneous data structures, with an accentuated geo-spatial component. Within this scope, this thesis attempts to develop concepts and fundamental theories that make sketching useful for applications in the GISs domain.; To evaluate the practicability of sketching for modern human-computer interaction we have analyzed the process of interaction on different levels and from various perspectives. The interpretation of a survey that required human subjects to draw sketches according to written scenarios provided valuable information about people's sketching habits and strategies. Based on these observations we have developed a formal model of a sketch. The basic building blocks of this model are sketched objects and a subset of relevant, binary spatial relations. This subset is obtained by considering only relations between objects that are Voronoi neighbors. Relations are based on the topology, metric, and direction relationship between object pairs. Objects are described by geometric attributes. To prove our concepts we have implemented a software prototype of a sketch-based query user interface for GISs. This application can be used to draw sketches and query them against a simple, sketch database. The result is a ranked list of sketches that are conceptually similar to the sketched query.; We have observed that people use fairly simple and abstract objects in their sketches and we have shown that it is feasible to interpret and translate a sketched scene into a form that can be used to query a spatial database. We can, therefore, expect that sketching is an expressive modality and a realistic enhancement for applications where spatial information has to be browsed, queried, or updated, such as in a GIS. |
