CaGIS Vol. 27, No. 1 (Jan 2000)

Guidelines for the Display of Attribute Certainty

Michael Leitner and Barbara P. Buttenfield

This research investigates how the inclusion of attribute certainty in map displays influences GIS modeling and spatial decision support. The goal is to establish empirical evidence documenting graphical guidelines that can be incorporated as GIS system defaults for mapping depiction of attribute certainty. These three variables, in addition to the level of map detail, are depiction of attribute certainty. These three variables, in addition to the level of map detail, are explored in this research. A hypermedia document had been developed to simulate decision makers’ use of certainty information for two locational siting tasks: the correctness, time, and confidence of both siting decisions. The experiment further determines how variations in symbolizing attribute certainty (by value, saturation, or texture) affect the three variables of correctness, time, and confidence. A third goal focuses on whether the difficulty of the task affects the decision. On a theoretical level, this research uncovers new information about assimilating data quality information into spatial decision support. On a practical level, it establishes symbolization schemes for representing attribute certainty on thematic maps. These should be incorporated as GIS graphical defaults in anticipation of digital data sets that include data quality information. This research is a continuation of a long-standing tradition of empirical research in map design as a paradigm for eliciting and formalizing cartographic knowledge.

The Search for Boundaries on Maps: Color Processing and Map Pattern Effects

Rick Bunch and Robert Lloyd

Keates (1982) argues that map reading could be considered as a number of map-use tasks that take place in the process of obtaining desired information. These tasks are often related and, frequently, the result produced by an earlier task becomes input for a later test.

Three-dimensional Reconstruction of the Yaolin Cave

Jianhua Gong, Hui Lin, and Xiaolu Yin

This paper reports on three-dimensional reconstruction of the Yaolin Cave in the Karst Region of Zhejiang, China. An object-oriented method was used to represent two cave classes--the class Boundary and the class Inside. The class Boundary included objects of the cave ceiling and the cave floor which are part of the topographical trend of the cave. This trend was determined by integrating topography with landform using TIN modeling. The inside of the cave with stalagmites, stalactites, dripstone-columns, and other objects was built using surveying data, photographs, and such computer graphics techniques as texture mapping and transparency. A stand-alone, 3-D visualization system-Cave3D-was developed in the Windows 98/NT platform to produce 3-D graphics and implement graphics-based computation, spatial query, and analyses. A virtual Yaolin cave was created using VRML97 and Java and posted on the Web.

Knowledge Acquisition for Generalization Rules

Tiina Kilpelainen

How to replace the human element of generalization with computer algorithms or rules in knowledge bases has been frequently discussed, but we have not succeeded in formulating these rules very well. The purpose of this article is to illustrate the problem of knowledge acquisition for generalization of topographic maps. Three studies to derive rule-based knowledge for automatic map generalization are presented and analyzed. In the tests, cartographers were asked to interpret map objects to be generalized and to describe the basis of their decisions. The studies showed that by interviewing cartographers, much of the domain knowledge can be gathered, but the most time-consuming part of documenting this knowledge is to analyze the data and formalize the results. It was also found that there is important domain knowledge on generalization that has not previously been documented. The tests performed resulted in the discovery of four categories of declarative rules: geometric, topological, context-related, and culture-related rules.

Perception of Spatial Dispersion in Point Distributions

Yukio Sadahiro

This paper analyzes the perception of spatial dispersion on point distributions. Spatial dispersion is one of the major concepts communicated by dot maps. To promote efficient communication of this concept, two experiments were conducted to investigate the relationship between the perception of spatial dispersion and such map characteristics as spatial arrangement of points, number of points, symbol size, and map scale. Regression models were built on the basis of the experimental results to describe the relationship quantitatively. The obtained models enable map authors to predict the degree of spatial dispersion perceived by map readers. From the models and the results of a computer-assisted simulation, the following conclusions were obtained: 1) map scale greatly affects the perception of spatial dispersion; 2) spatial arrangement of points and number points are also influential; 3) the size of point symbols does not significantly affect the perception of spatial dispersion.

Solving Space Conflicts in Map Generalization: Using a Finite Element Method

Peter Hojholt

A finite element method was developed to handle conflicts during the generalization of maps. The method is holistic and solves conflict problems for the entire map surface simultaneously. When a generalized object changes size, the method immediately causes displacements in surrounding objects. Boundary constraints were introduced which make it possible to maintain the shape of objects, and simultaneously change the size of objects. An iterative solution procedure for the Finite Element problem was shown to give solutions that better fulfill topological requirements than a direct solution of the problem.

A Component Perspective on Geographic Information Services

Bin Li

This paper explores the notions of geographic information services in the context of component technology. It suggests that componentization gives rise to an alternative view on GIS as geographic information services. The change from monolithic systems to component-oriented systems requires examination of the service structure of GIS. This paper presents a general discussion on the notions of component and services. A combination of existing reference models of information services and an empirical model of software evolution is used to identify geographic information services. Application services, functional services, and common services are considered to the main groups of information services in the component architecture. The discussion focuses in the functional services and common services in the component architecture. The discussion focuses on the functional services and common services within the domain of geographic information processing. Eight groups of such services are identified. They represent a reorganization of geographic information services in light of recent advances in component technology. The service structure is substantially different from the functional components of traditional GIS. The requirement for inter-operation adds several groups of common services, including data access, catalog, transformation, and registry. Developing the components for geographic information services presents both technical and theoretical challenges. In the theoretical domain, the problem of representation is crucial for achieving high levels of interoperability. The concepts are further elaborated through an example on how component technology makes it easy to use advanced geographic techniques through a distributed spatial statistical modeling service.