Denis J. Dean

IDENTIFYING GAPS IN CONSERVATION NETWORKS: OF INDICATORS AND UNCERTAINTY IN GEOGRAPHIC‐BASED ANALYSES

Mapping of biodiversity elements to expose gaps in conservation networks has become a common strategy in nature-reserve design. We review a set of critical assumptions and issues that influence the interpretation and implementation of gap analysis, including: (1) the assumption that a subset of taxa can be used to indicate overall diversity patterns, and (2) the impact of uncertainty and error propagation in reserve design. We focus our review on species diversity patterns and use data from peer-reviewed literature or extant state-level databases to test specific predictions implied by these assumptions. Support for the biodiversity indicator assumption was varied. Patterns of diversity as reflected in species counts, coincidence of hot spots, and representativeness were not generally concordant among different taxa, with the degree of concordance depending on the measure of diversity used, the taxa examined, and the scale of analysis. Simulated errors in predicting the occurrence of individual species indicated that substantial differences in reserve-boundary recommendations could occur when uncertainty is incorporated into the analysis. Furthermore, focusing exclusively on vegetation and species distribution patterns in conservation planning will contribute to reserve-design uncertainty unless the processes behind the patterns are understood. To deal with these issues, reserve planners should base reserve design on the best available, albeit incomplete, data; should attempt to define those ecological circumstances when the indicator assumption is defensible; should incorporate uncertainty explicitly in mapped displays of biodiversity elements; and should simultaneously consider pattern and process in reserve-design problems.

Comparative accuracies of artificial neural networks and discriminant analysis in predicting forest cover types from cartographic variables

This study compared two alternative techniques for predicting forest cover types from cartographic variables. The study evaluated four wilderness areas in the Roosevelt National Forest, located in the Front Range of northern Colorado. Cover type data came from US Forest Service inventory information, while the cartographic variables used to predict cover type consisted of elevation, aspect, and other information derived from standard digital spatial data processed in a geographic information system (GIS). The results of the comparison indicated that a feedforward artificial neural network model more accurately predicted forest cover type than did a traditional statistical model based on Gaussian discriminant analysis.

Trauma Exposure and Posttraumatic Stress Disorder Among Employees of New York City Companies Affected by the September 11, 2001 Attacks on the World Trade Center

OBJECTIVE Several studies have provided prevalence estimates of posttraumatic stress disorder (PTSD) related to the September 11, 2001 (9/11) attacks in broadly affected populations, although without sufficiently addressing qualifying exposures required for assessing PTSD and estimating its prevalence. A premise that people throughout the New York City area were exposed to the attacks on the World Trade Center (WTC) towers and are thus at risk for developing PTSD has important implications for both prevalence estimates and service provision. This premise has not, however, been tested with respect to DSM-IV-TR criteria for PTSD. This study examined associations between geographic distance from the 9/11 attacks on the WTC and reported 9/11 trauma exposures, and the role of specific trauma exposures in the development of PTSD. METHODS Approximately 3 years after the attacks, 379 surviving employees (102 with direct exposures, including 65 in the towers, and 277 with varied exposures) recruited from 8 affected organizations were interviewed using the Diagnostic Interview Schedule/Disaster Supplement and reassessed at 6 years. The estimated closest geographic distance from the WTC towers during the attacks and specific disaster exposures were compared with the development of 9/11-related PTSD as defined by the Diagnostic and Statistical Manual, Fourth Edition, Text Revision. RESULTS The direct exposure zone was largely concentrated within a radius of 0.1 mi and completely contained within 0.75 mi of the towers. PTSD symptom criteria at any time after the disaster were met by 35% of people directly exposed to danger, 20% of those exposed only through witnessed experiences, and 35% of those exposed only through a close associates direct exposure. Outside these exposure groups, few possible sources of exposure were evident among the few who were symptomatic, most of whom had preexisting psychiatric illness. CONCLUSIONS Exposures deserve careful consideration among widely affected populations after large terrorist attacks when conducting clinical assessments, estimating the magnitude of population PTSD burdens, and projecting needs for specific mental health interventions.

An Investigation into the Causes of Errors and Inconsistencies in Predicted Viewsheds

Previous evaluations of viewshed analyses have raised concerns about the accuracy and repeatability of the process. Digital elevation model (DEM) errors, the limited spatial resolution of DEMs, and differing algorithms employed by different GIS packages have all been suggested as possible sources for inaccuracy and nonrepeatability. This study compared a field surveyed viewshed to predicted viewsheds generated using a variety of software packages and DEM databases, some of which contained known amounts of error. We found that each of the factors suggested by previous authors contributes to errors in predicted viewsheds. DEM errors contribute most to the discrepancies between surveyed and predicted viewsheds, and the majority of their negative impact occurred at very low levels of DEM error. Differing algorithms used by different GIS packages also contribute significantly to surveyed/ predicted viewshed discrepancies, but more importantly, result in predicted viewsheds that disagree with one other, thereby confounding comparisons of results generated with differing software systems. Finally, the spatial resolution of DEMs also has a significant effect on the degree of agreement between surveyed and predicted viewsheds, but the magnitude of this effect is not as great as are the effects produced by DEM errors.

Optimal Routefinding with Unlimited Possible Directions of Movement

Finding optimal paths through raster databases is limited by the very nature of the raster data itself. This limitation restricts the possible directions of movement through the database from the infinite possibilities found in the real world to a finite number of possibilities defined by the cell-to-cell movement that characterizes raster databases. A Triangulated Irregular Network (TIN)-based alternative optimization model that allows unlimited possible directions of movement is presented. While not without its own limitations, this new approach offers a viable alternative to raster-based optimal routefinding.

Modeling the magnitude and spatial distribution of aesthetic impacts

Timber-harvesting operations, especially clearcutting (that is, harvesting operations where all of the trees in a given area are removed), have been criticized for many reasons, not least of which is their unsightly appearance. Forest managers have recognized this, and have attempted to place clearcuts in locations with limited viewsheds. In order to find such locations, forest managers have made extensive use of standard geographical information system (GIS) viewshed operations. The use of conventional viewshed operations ignores the possibility that the aesthetic impacts of clearcuts might be diminished by the screening effects of intervening vegetation, or the possibility that impacts simply decrease with increasing distance. In this study we found evidence that the aesthetic impacts of clearcuts do in fact diminish in these ways. Photograph transects were performed around ten clearcuts. Each transect produced a series of pictures showing the clearcut from increasing distances into the surrounding forest. The Law of Comparative Judgments (LCJ) technique was used to develop perceived-scenic-beauty rankings for each photograph. Statistical analyses showed aesthetic impacts do in fact diminish with viewing distance through screening vegetation. A modified viewshed algorithm was then developed not just to identify areas where clearcuts are visible, but also to map localized aesthetic impacts of clearcuts. The approach presented here could be used to develop similar models that map the aesthetic impacts of any proposed environmental modification.

Characterizing Spatial Databases via their Derivation: A Complement to Content Ontologies

Developing an ontology that succinctly describes the contents of a spatial database is a very difficult undertaking. Yet most current efforts to develop spatial ontologies remain focused on describing content. Ontologies describing other aspects of spatial databases may prove to be much easier to develop and nearly as useful as content ontologies, and yet these alternative ontologies have received little attention from the research community. This paper explores one such alternative, specifically, an ontology that describes how a spatial database may have been derived. Derivation ontologies are shown to be highly complementary to content ontologies, and in some cases can perform nearly identical tasks. It is also shown that derivation ontologies are much more straightforward to develop than are content ontologies. Finally, we present a genetic programming (GP)-based approach to automatically developing derivation ontologies for existing databases. It is concluded that while derivation ontologies cannot replace content ontologies, they are a useful and practical complement that offer their own unique set of strengths to the problem of semantically characterizing spatial data. Ke

Measuring arrangement similarity between thematic raster databases using a quadtree-based approach

Measuring the degree of similarity between thematic raster databases is a common task widely used in remote sensing accuracy assessment, spatial model validation, and many other geospatial tasks. However, conventional similarity measures look only at point-to-point similarity; they are not designed to evaluate the similarity of shapes and arrangements of features within the databases being compared. This study proposes a technique of assessing arrangement similarity based on a comparison of quadtree representations of the maps being evaluated. Empirical assessment shows that the technique produces results that agree strongly with subjective evaluations of the similarity of artificial raster databases produced by a survey of map users.

Optimal Routefinding Across Landscapes Featuring High-cost Linear Obstacles

Existing GIS-based least-cost routefinding approaches can in some cases be confounded by linear features in the landscape whose crossing costs are high relative to other traversing costs found throughout the landscape. Unfortunately, such high-cost linear features are not uncommon; they frequently occur in the form of hydrologic features whose crossing costs are high relative to costs of traversing the surrounding dry land. This study (1) enumerates the situations where existing approaches can fail, (2) proposes a simple method for overcoming the limitations of the existing approaches, and (3) conducts an experiment to assess the impact of the weaknesses of existing approaches and the magnitude of the differences between the results produced by existing and revised approaches. Our results show that in mountainous terrain, linear hydrologic features with high crossing costs can have a profound impact on least-cost routes, and the choice of solution method has equally profound impacts on the optimal route produced by the analysis.

Spatial optimization for regionalization problems with spatial interaction: a heuristic approach

Spatial optimization techniques are commonly used for regionalization problems, often represented as p-regions problems. Although various spatial optimization approaches have been proposed for finding exact solutions to p-regions problems, these approaches are not practical when applied to large-size problems. Alternatively, various heuristics provide effective ways to find near-optimal solutions for p-regions problem. However, most heuristic approaches are specifically designed for particular geographic settings. This paper proposes a new heuristic approach named Automated Zoning Procedure-Center Interchange (AZP-CI) to solve the p-functional regions problem (PFRP), which constructs regions by combining small areas that share common characteristics with predefined functional centers and have tight connections among themselves through spatial interaction. The AZP-CI consists of two subprocesses. First, the dissolving/splitting process enhances diversification and thereby produces an extensive exploration of the solution space. Second, the standard AZP locally improves the objective value. The AZP-CI was tested using randomly simulated datasets and two empirical datasets with different sizes. These evaluations indicate that AZP-CI outperforms two established heuristic algorithms: the AZP and simulated annealing, in terms of both solution quality and consistency of producing reliable solutions regardless of initial conditions. It is also noted that AZP-CI, as a general heuristic method, can be easily extended to other regionalization problems. Furthermore, the AZP-CI could be a more scalable algorithm to solve computational intensive spatial optimization problems when it is combined with cyberinfrastructure.