Visualizing Accessibility with GIS

Introduction As the environmental, social, and health costs of sprawling, automobile dependent development patterns become well understood, accessibility, or walkability, becomes a significant goal of planners, policy makers, and citizens. Our current planning environment is one of auto-mobility, which has the goal of reducing the cost per mile of travel within a metropolitan area. An automobility approach may find success for a 15 minute commute that travels fifteen miles at speeds of sixty plus miles per hour – the cost per mile is relatively low in terms of time and delay. Similarly, an auto-mobility approach to regional travel would be considered a failure when congestion inhibits automobile travel from traveling at maximum speed limits; the cost per mile becomes quite high on account of time delays in traffic. In contrast, an accessibility focus of development seeks to help people gain access to their destinations at a low cost per trip. In an accessibility-centered approach, popular places to visit cause increased numbers of people on sidewalks and in street intersections. These increases in turn tend to slow down the speeds of automobiles in the area. There is a tradeoff of mobility that favors the pedestrian rather than the automobile. Developers and planners are increasingly incorporating such tradeoffs involving pedestrian accessibility into their visions and plans. They tend to base their decisions on a variety of principles, including increased quality of life, more active community interaction, environmental benefits of reduced automobile dependence, and congestion reduction. These principles are often characterized, in part at least, under a variety of terms: "New Urbanism," "Neotraditional Planning," "Pedestrian Pockets," "Transit Oriented Development," or "Nodal Development." The claimed or potential benefits of these schemes is beyond the scope of the current discussion. The focus here is on visualizing accessibility principles: to visualize is to clarify. What are the various ways that one can visualize accessibility using Geographic Information