Thomas J. Cova

A network flow model for lane-based evacuation routing

Most traffic delays in regional evacuations occur at intersections. Lane-based routing is one strategy for reducing these delays. This paper presents a network flow model for identifying optimal lane-based evacuation routing plans in a complex road network. The model is an integer extension of the minimum-cost flow problem. It can be used to generate routing plans that trade total vehicle travel-distance against merging, while preventing traffic crossing-conflicts at intersections. A mixed-integer programming solver is used to derive optimal routing plans for a sample network. Manual capacity analysis and microscopic traffic simulation are used to compare the relative efficiency of the plans. An application is presented for Salt Lake City, Utah.

Towards a general theory of geographic representation in GIS

Geographic representation has become more complex through time as researchers have added new concepts, leading to apparently endless proliferation and creating a need for simplification. We show that many of these concepts can be derived from a single foundation that we term the atomic form of geographic information. The familiar concepts of continuous fields and discrete objects can be derived under suitable rules applied to the properties and values of the atomic form. Fields and objects are further integrated through the concept of phase space, and in the form of field objects. A second atomic concept is introduced, termed the geo‐dipole, and shown to provide a foundation for object fields, metamaps, and the association classes of object‐oriented data modelling. Geographic dynamics are synthesized in a three‐dimensional space defined by static or dynamic object shape, the possibility of movement, and the possibility of dynamic internal structure. The atomic form also provides a tentative argument that discrete objects and continuous fields are the only possible bases for geographic representation.

Microsimulation of neighborhood evacuations in the urban - wildland interface

Residential development in fire-prone wildlands is occurring at an unprecedented rate. Community-based evacuation planning in many areas is an emerging need. In this paper we present a method for using microscopic traffic simulation to develop and test neighborhood evacuation plans in the urban–wildland interface. The method allows an analyst to map the subneighborhood variation in household evacuation travel times under various scenarios. A custom scenario generator manages household trip generation, departure timing, and destination choice. Traffic simulation, route choice, and dynamic visualization are handled by a commercial system. We present a case study for a controversial fire-prone canyon community east of Salt Lake City, Utah. GIS was used to map the spatial effects of a proposed second access road on household evacuation times. Our results indicate that the second road will reduce some household travel times much more than others, but all evacuation travel times will become more consistent.

Modelling community evacuation vulnerability using GIS

We present a method for systematically identifying neighbourhoods that may face transportation di Yculties during an evacuation. A classi® cation of this nature o Vers a unique approach to assessing community vulnerability in regions subject to fast-moving hazards of uncertain spatial impact (e.g., urban ® restorms and toxic spills on highways). The approach is founded on an integer programming (IP) model called the critical cluster model (CCM). An heuristic algorithm is described which is capable of producing e Ycient, high-quality solu- tions to this model in a GIS context. The paper concludes with an application of the method to Santa Barbara, California.

Extending geographical representation to include fields of spatial objects

This paper describes a means for linking field and object representations of geographical space. The approach is based on a series of mappings, where locations in a continuous field are mapped to discrete objects. An object in this context is a modelers conceptualization, as in a viewshed, highway corridor or biological reserve. An object can be represented as a point, line, polygon, network, or other complex spatial type. The relationship between locations in a field and spatial objects may take the form of one-to-one, one-to-many, many-to-one, or many-to-many. We present a typology of object fields and discuss issues in their construction, storage, and analysis. Example applications are presented and directions for further research are offered.

MAPPING EVACUATION RISK ON TRANSPORTATION NETWORKS USING A SPATIAL OPTIMIZATION MODEL

The focus of this paper is on the development of a methodology to identify network and demographic characteristics on real transportation networks which may lead to significant problems in evacuation during some extreme event, like a wildfire or hazardous material spill. We present an optimization model, called the critical cluster model, that can be used to identify small areas or neighborhoods which have high ratios of population to exit capacity. Although this model in its simplest form is a nonlinear, constrained optimization problem, a special integer-linear programming equivalent can be formulated. Special contiguity constraints are needed to keep identified clusters spatially connected. We present details on how this model can be solved optimally as well as discuss computational experience for several example transportation networks. We describe how this model can be integrated within a GIS system to produce maps of evacuation risk or vulnerability. This model is now being utilized in several research projects, in Europe and the US.

Setting Wildfire Evacuation Trigger Points Using Fire Spread Modeling and GIS

Warning communities in the path of an advancing wildfire is a challenging problem. Decision makers need the most current information available to determine who should evacuate, when they should leave and what type of order to issue (e.g. mandatory, recommended, voluntary). This paper presents a new method for delimiting wildfire evacuation trigger points using fire spread modeling and GIS. Using data on wind, topography, and fuel in conjunction with estimated evacuation time, a trigger buffer can be computed for a community whereby an evacuation is recommended if a fire crosses the edge of the buffer. A case study is presented for the Corral Canyon section of the 1996 Calabasas Fire near Malibu, California, USA. The paper concludes with a discussion of the strengths and weaknesses of this approach.

EDGIS: a dynamic GIS based on space time points

Contemporary GIS can handle static spatial data for querying and visual representation, but the temporal dimension remains a challenge. This paper addresses the need for a dynamic GIS capable of managing complex data types. The design relies on a representation of the theoretical spatiotemporal primitive known as the ‘geo-atom’. This paper proposes a novel and implemented data structure called the space time point (STP) built on this theory. With the STP representation, spatiotemporal data queries can be posed to return useful results about dynamic geographic phenomena and their interaction. Two key challenges addressed in this research are (1) data structures to represent hybrid (object and field) spatiotemporal phenomena and (2) the design of a dynamic GIS interface. These challenges are addressed by the implementation of the system, referred to as ‘Extended Dynamic GIS (EDGIS)’, that uses the proposed STPs. The EDGIS system is described from theory to its implementation in Java™ and a series of application examples are described followed by performance metrics. The paper concludes with a discussion of areas for further research such as integration of the system with geo-sensor networks, hazards, transportation, and location-based services (LBS).

Exurban Change Detection in Fire-Prone Areas with Nighttime Satellite Imagery

Fire-prone landscapes are increasingly being settled. Monitoring this development is an emerging need, and a low-cost method would benefit emergency managers. Existing changedetection methods can be expensive and time consuming when applied to low-density urban change in large, vegetated areas. Nighttime satellite imagery is explored as means for addressing this problem, and a case study is presented for Colorado. The results indicate that from 1992‐2000, Grand County had the greatest absolute increase in ambient sprawl into fire-prone areas (215 km 2 ), but Teller County had the greatest percentage increase (7.3 percent). In 2000, La Plata County had the most ambient development in fire-prone areas (909 km 2 ), but Jefferson County had the greatest percentage (42 percent). The paper concludes with a discussion of the prospects and problems of the approach.

Exploratory spatial optimization in site search: a neighborhood operator approach

Simultaneously locating and configuring the best site for a given land use or activity is a complex planning problem. This paper describes a method for addressing this problem that relies on a point-to-area neighborhood operator applied to a raster model of geographic space. This represents a synthesis of concepts drawn from cartographic modeling, optimal land allocation, and suitability mapping. The approach generates a mathematical field of best site boundaries that we call a site field. A site field does not lend itself to static visualization in two dimensions, and an interface for interactively exploring its contents is described. A significant benefit of adopting a neighborhood operator approach is that it serves to spatially decompose the global site search problem into a set of smaller, local problems. Therefore, the computational effort required to solve an optimal site search problem for a given cell in a raster representation of space is not tied to the number of cells in the global data set.