Donald G. Janelle
This paper reviews space-time properties of urban structure with regard to developments in transportation and communications. Space-adjusting technologies, in combination with the timing of land uses and activities, are shown to impart discontinuities in the topology of urban regional structure. Such discontinuities influence the formation of parallel, but different, activity patterns in the daily lives of representative urban subpopulations and contribute to continually changing density patterns of human occupance at different times of the day. Examples of these phenomena are illustrated for North American cities. The importance of being able to visualize rapid changes in these patterns is presented as an important challenge for applications in Geographic Information Science. The ability to identify these patterns has important practical significance regarding planning issues and has implications for the development of sound academic understanding of relationships between urban social and spatial structures.
CONTRIBUTORS TO SPACE-TIME DISCONTINUITIES IN URBAN REGIONS:
Two factors are particularly significant in distorting the space- time structures of cities and their regions. The first is the differential use of the time dimension by specific land use activities, sometimes referred to as the "timing of space." The second involves space adjusting technologies that alter the significance of distance in peoples' choice of activities.
The Timing of Space:
The timing of space, a concept proposed by Parkes and Thrift (1975), refers to the opening hours of establishments; some banks are open from 8:00 a.m. to 8:00 p.m., others from 10:00 a.m. to 4:00 p.m.; some restaurants and grocery stores may be open for 24 hours a day, while others set more limited schedules for customer access. When the lights go out, they no longer serve as part of the activity system for the urban resident. In a typical North American city of 300,000 people, several thousand such timing decisions occur daily. Some conform to set societal standards for the timing of work, schools, and other activity sites. But, increasingly, the temporal ordering of cities has become more diverse and less predictable.
Policy options to mediate congestion on city streets have encouraged large employers to stagger the work hours of employees; other employers have responded to changing needs of employee groups (e.g., workers from two-income households and single-parent workers) by introducing flexible work-hour arrangements. The "colonization of time," particularly night time, is a concept advanced by Melbin (1978) to refer to the increasingly long opening hours of many establishments; but, in addition, there is evidence of an increasing number of activities that practise temporal specialization -- e.g., "breakfast-only" restaurants, and "lunch" shops, etc. In contrast to the traditional norm of standard 8-hour work days, there is considerably more diversity and independence in the timing of activities within cities of the late 1990s.
For any particular time of the day, one can envision a supply of accessible (i.e., open) activity sites of a given category (e.g., pharmacies, gymnasiums, bars). In the aggregate, these timing decisions have considerable impact on the overall movement patterns of populations for commuting, shopping, recreating, and other activities. Surprisingly, there are no systematic databases that describe this phenomenon for individual North American cities.
The Role of GIS. Could an active on-line GIS representation incorporate information of the timing of the city and its parts? Would this be of value to landuse planners, traffic engineers, bus route planners, emergency health care, policing, and fire protection units, marketers of consumer products and services, and others? In a fully wired city, could this information be signalled on occurrence of the opening and closing of establishments? Could this information be accessibly via home computers to households as well as public agencies?
Such a GIS database might be used to increase our understanding of urban social issues. For example, how do the time supplies of activities differ in accessibility for different subpopulations in different parts of the urban environment? Would such a database allow us to isolate categories of temporal coordination and compatibility problems that are specific to gender, age, ethnicity, and income, to shift-workers versus part- time employees, two-worker households versus one-worker-two- parent households, or single-parent households? As noted by Burns (1979) temporal considerations are fundamental to the whole issue of accessibility and opportunity in the modern city. Some of the most significant social issues of the modern city are represented in current political debate over the temporal ordering of urban life, particularly as seen in the conditions of employment and the timing of affordable childcare (Janelle, 1993). Representing the city around the clock is critical to understanding its reality and to dealing effectively with its structural and social problems.
Distorting Space-time Relationships and Visualizing the Impacts of Space-adjusting Technologies
The timing of spaces is a determinant in the accessibility to opportunities, but the ability to move from one location to another is a related complementary problem. For this reason, representations on the temporal patterns of activity sites should be coupled with indications of how transportation and communications technologies permit access to such sites from throughout an urban region.
Travel time is commonly regarded as the single-most significant indicator on the impact of transportation-based innovation. Yet, from analytical and visualization perspectives, it poses considerable difficulties. Reasons for this include:
Isochrone maps are commonly used for visualizing the impacts of change in transportation systems over time. However, such maps, even the more refined time-distance transformations developed by Clark (1977) for Seattle and Muller (1978) for Edmonton, suffer significant limitations:
This example illustrates that locations at the urban edge converge in time-space more rapidly with other places in the city than either the center or any points intermediate between the center and the edge. This transfer of transport accessibility advantages from the centers to the edges of cities needs documentation in regards to economic and social implications. Traditional analytical focus on notions of absolute space hide such profound topological restructuring of cities. In contrast, functional measures of distance (e.g., cost and time) illustrate clearly how space is transformed in response to investments in transport infrastructure. The detection of such changes require an extension of data requirements, and a perfection of means to appropriately illustrate alternative geographical concepts regarding the changing space-time structures of cities.
The Role of GIS. How can GIS incorporate visualizing capabilities to capture the changing nature of transportation's impact on city structure? While representations of complex and ever-changing geometries may defy analytical solutions, the capability for rapid transformation of a basic database into a host of different representations is a powerful option. In order of complexity and data requirements, these representations might include:
Discussion:
This paper presents two areas of need in the effort to refine our understanding of human activity patterns in cities. The first is to monitor the opening and closing of activity sites within cities and the second is to depict, by functional measures of distance, the effort required to move between activity sites within urban areas. Both of these factors impinge on the freedom of accessibility of urban residents. They both contribute to the time-geography of urban life, defining the opportunities and constraints that distinguish social groupings and different regions of the city.
Just as it is important to know how the time supplies of activities differ in accessibility for different subpopulations in different parts of the urban environment, it is also important to understand how well different client groups are served by the transportation options. To what extent do changing transportation and communication environments solve or create accessibility problems for individuals with variable conditions of constraint because of employment, household responsibility, health, and limitations on mobility? There is need to depict the travel environments for diverse client groupings. Captive riders of bus systems, voluntary users of public transportation, people dependent on para-transit services, automobile users, bicyclists, and pedestrians all have different patterns of accessibility. As with the activity sites in the city, public transportation services are often constricted to certain periods of the day and to disparate schedules and routes. These alternative transportation environments need to be identified. The multiple time-space realities for different populations need representation and comparison. Can Geographic Information Science help?
References:
Angel, S. and Hyman, G.M. 1976 Urban Fields: A Geometry of Movement for Regional Science (London: Pion Ltd).
Bunge, W.W. 1966 Theoretical Geography, Second Edition, Lund Studies in Geography, Series C, General and Mathematical Geography I (Lund: Gleerup).
Burns, L.D. 1979 Transportation, Temporal and Spatial Components of Accessibility (Lexington, MA: Lexington Books).
Clark, J.W. 1977 "Time-distance Transformations of Transportation Networks" Geographical Analysis 9:195-205.
Ewing, G.O. 1974 "Multidimensional Scaling and Time-space Maps" The Canadian Geographer 18:161-7.
Ewing, G. and Wolfe, R., 1977 "Surface Interpolation on Two dimensional Time-space" Environment and Planning A 9:429-37.
Forer, P. 1978. "A Place for Plastic Space" Progress in Human Geography 3:230-67.
Gatrell, A. 1983. Distance and Space: A Geographical Perspective (Oxford: Clarendon Press).
Janelle, D.G. 1968 "Central Place Development in a Time-space Framework" The Professional Geographer 20:5-10.
Janelle, D.G. 1993 "Urban Social Behaviour in Time and Space" in Larry S. Bourne and David F. Ley (eds.) The Changing Social Geography of Canadian Cities (Montreal and Kingston: McGill- Queen's University Press) 103-18.
Janelle, D.G., 1995 "Metropolitan Expansion, Telecommuting, and Transportation," in Susan Hanson (ed.) The Geography of Urban Transportation, 2nd ed. (New York: Guilford Press) 407-34.
Melbin, M. 1978. "The Colonization of Time" in T. Carlstein, D.N. Parkes, and N.J. Thrift (eds.) Human Activity and Time Geography, vol. 2 (London: Edward Arnold) 100-13.
Muller, J.C. 1978. "The Mapping of Travel Time in Edmonton, Alberta" The Canadian Geographer 22:195-210.
Parkes, D.N., and N. J. Thrift 1975 "Timing Space and Spacing Time" Environment and Planning A 7: 651-70.