Experiments in interactive map retrieval
Thesis DisciplineComputer Science
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The thesis deals with the problem of constructing an interactive, visual browser for a large database of geographic data. Results are presented from work in two areas: one area is that of graphical user interfaces, the other is the structuring of a geographic database for rapid retrieval of information for interactive display. The design is discussed of a user interface for a map browsing system. Proposals are then made about how a map database should appear to the user, and the functions that a map browsing system should provide. Observations are made about user interface systems in general. Particular reference is made to the difficulty, with present user interface systems, of ensuring consistency of the style, or "look and feel", of the user interface between applications, and of allowing the style to be customised to suit user preferences. An architecture for user interface systems is proposed in which applications are independent of the style of the user interface, so that the user may change the style at will. Suggestions are made as to how such a system might be realised. The NeWS extensible window server, based on the PostScript graphics programming language, is examined. Some characteristics of PostScript are identified which make this language attractive for the task of displaying maps. Possibilities offered by NeWS for customisable user interfaces are explored. To overcome the difficulties in writing large PostScript programs by hand, the author devised a new language P. A user interface toolkit for NeWS, written by the author in P, is described. Use of P made the task of writing the toolkit much easier. General observations are made about the design of such toolkits in the NeWS environment. Suggestions are made for improving the NeWS server-client communication model and support tools. The second part of the thesis discusses the design of geographic databases. Some extensions are suggested to general geographic data models to support the specific requirements of interactive browsing. Results are presented from a set of experiments with different techniques of implementing these extensions. Implementations are compared of several spatial indexing methods in a relational database environment. Locality of reference in map browsing is discussed. Experimental assessments are made of the following methods for exploiting this locality: clustering, caching, and pre-fetching. From the results of these experiments, conclusions are drawn about how to efficiently organise and index spatial data for interactive browsing in a conventional relational database system. Many of these conclusions are applicable in general to other forms of database management system.