Summary

With the increasing use of the Internet as a medium for getting information, transacting business and interacting with people, a wide range of activities in everyday life can now be undertaken in cyberspace. As traditional models of accessibility are based on physical notions of distance and proximity, they are inadequate for conceptualizing or analyzing individual accessibility in the physical world and cyberspace (hereafter referred to as "hybrid-accessibility"). To address the need for new models of space and time that enable us to grapple with the problem of individual accessibility in the information age, there are at least three major research areas: (a) the conceptual and/or behavioral foundation of individual accessibility; (b) appropriate methods for representing accessibility; and (c) feasible operational measures for evaluating individual accessibility. With the recent development and application of GIS methods in the study of accessibility in the physical world (e.g. Forer 1998; Hanson et al 1998; Huisman and Forer 1998; Kwan 1998, 1999a,b; Miller 1991, 1999; Scott 1999; Talen 1997; Talen and Anselin 1998), it is apparent that GIS have considerable potential in each of these research areas. As shown in some of these studies, a focus on the individual enabled by GIS methods also reveals the spatial-temporal complexity in individual activity patterns and accessibility through 3D visualization or computational procedures. 

Yet, even with the advent of 3D GIS tools in recent years, there are several difficulties when GIS methods are applied to represent or measure individual hybrid-accessibility. First, personal accessibility in the age of information involves multiple spatial and temporal scales (Hodge 1997), whereas current GIS are designed to handle only one geographical and/or temporal scale at a time. For instance, personal extensibility enabled by telecommunication technologies now allows an individual to access information resources at the global scale although the person's physical activities are still largely confined at the local scale. Further, the traditional temporal scale (hour/minute) is not adequate for studying cyber-transactions which may be accomplished within a few seconds. Second, GIS-based representational and computational methods such as the space-time prism are based on the sequential unfolding of a person's activities in the physical world. They are not developed to handle the simultaneity and temporal disjuncture that characterize many types of cyber-transactions. For example, a person may be talking over the phone and browsing a Web page at the same time. An email message sent out now may be read several hours later on the other side of the globe. These limitations of current GIS methods constitute a major challenge to any effort to represent and measure individual hybrid-accessibility in the information age.

As a preliminary attempt to address this methodological challenge, this paper explores how current GIS, given their limitations, can be deployed for the 3D interactive visualization of human extensibility in space-time. It develops and presents a method for the multi-scale, 3D representation of individual space-time paths based upon the concept of human extensibility (Janelle 1973; Adams 1995). Using the geo-referenced activity diary data of an individual as an example and ArcView 3D Analyst, the method is capable of revealing the spatial scope and temporal rhythms of a person's extensibility in cyberspace. It can also represent the complex interaction patterns among individuals in cyberspace using multiple and branching space-time paths within a GIS. Compared with the two-dimensional and/or cartographic representations in past studies, this method allows the researcher to interact, explore and manipulate the 3D scene (e.g. rotation, fly-through). This visualization environment not only greatly facilitates exploratory data analysis, but can also enhance our understanding of the patterns portrayed. It may provide the basis for formulating operational measures of individual hybrid-accessibility. In this paper, the nature of accessibility in the information age is first examined, and then alternative representational methods are discussed. Implementation of the GIS method using real activity diary data of an individual is finally described.