Python Scripting for ArcGIS is a guide to help experienced users of ArcGIS for Desktop get starte... more Python Scripting for ArcGIS is a guide to help experienced users of ArcGIS for Desktop get started with Python scripting. This book teaches how to write Python code that works with spatial data to automate geoprocessing tasks in ArcGIS. Readers can thus learn the skill set needed to create custom tools. The book contains 14 chapters, with the corresponding data and exercises on the accompanying DVD. A 180-day trial of ArcGIS 10.1 for Desktop software is also provided as an online download. Key topics in this book include: Python language fundamentals, Automating geoprocessing tasks, Exploring and manipulating spatial data, Working with geometries and rasters, Map scripting, Debugging and error handling, Creating functions and classes, and Creating and sharing script tools. More details on the book can be found at the Esri Press website: http://esriurl.com/5564. This includes sample chapters for download. Instructors who are considering the book as a textbook for a course can request a deskcopy from Esri Press: http://esripress.esri.com/offers/deskcopy.
Metropolitan WiFi positioning is widely used to complement GPS on mobile devices. WiFi positionin... more Metropolitan WiFi positioning is widely used to complement GPS on mobile devices. WiFi positioning typically has very fast time-to-first-fix and can provide reliable location information when GPS signals are too weak for a position fix. Several commercial WiFi positioning systems have been developed in recent years and most newer model smart phones have the technology embedded. This study empirically determined the performance of WiFi positioning system on two different mobile devices. Skyhook's system, running on an iPhone and a laptop, was selected for this study. Field work was carried out in three cities at a total of 90 sites. The positional accuracy of WiFi positioning was found to be very similar on the two devices with no statistically significant difference between the two error distributions. This suggests that the replicability of WiFi positioning on different devices is high based on aggregate performance metrics. Median values for positional accuracy in the three study areas ranged from 43 to 92 m. These results are similar to earlier independent evaluations of Skyhook's system. The number of access points (APs) observed on the iPhone was consistently lower than that on the laptop. This lower number of APs, however, was not found to reduce positional accuracy. In general, no relationship was found between the number of APs and positional accuracy for either device, counter to earlier findings. The results indicate, however, that WiFi positioning can be achieved with a small number of APs (5–10), but that increased numbers of APs do not contribute to improved positional accuracy. Despite the agreement in aggregate performance metrics between the two devices, the replicability of WiFi positioning using Skyhook's system in terms of getting the same location by using two different devices at approximately the same place and time was relatively poor. Implications for location-based services on mobile devices are discussed.
Global Positioning System devices are increasingly being used for data collection in many fields.... more Global Positioning System devices are increasingly being used for data collection in many fields. Consumer-grade GPS units without differential correction have a published horizontal positional accuracy of approximately 10–15 m (average positional accuracy). An attractive option for differential correction for these GPS units is the Wide Area Augmentation System (WAAS). Most consumer-grade GPS units on the market are WAAS capable. According to the Federal Aviation Authority (FAA), the WAAS broadcast message provides integrity information about the GPS signal as well as accuracy improvements, which are reported to improve accuracy to 3–5 m. Limited empirical evidence has been published on the accuracy of WAAS-enabled GPS compared to autonomous GPS. An empirical study was conducted comparing the horizontal and vertical accuracy of WAAS-corrected GPS and autonomous GPS under ideal conditions using consumer-grade receivers. Data were collected for 30-min time spans over accurately surveyed control points. Metrics of median, 68th and 95th percentile, Root Mean Squared Error (RMSE), and average positional accuracy in the horizontal and vertical dimensions were computed and statistically compared. No statistically significant difference was found between WAAS and autonomous position fixes when using two different consumer-grade units. When using WAAS, a third unit type exhibited a statistically significant improvement in positional accuracy. Analysis of data collected for a 27-h time span indicates that while WAAS is altering the estimated position of a point compared to an autonomous position estimate, WAAS augmentation actually appears to decrease the positional accuracy.
The Florida panther (Puma concolor coryi) is a relatively well studied species and it is well est... more The Florida panther (Puma concolor coryi) is a relatively well studied species and it is well established that the most important threat to panthers include limited habitat area and continued habitat loss and fragmentation. Despite the recognition that roads result in panther mortality and may limit panther movement there has been very limited research on the importance of roads. In the current study panther telemetry data from 1981 until 2004, detailed road networks and vegetation maps were used to determine vehicle-related mortality and road crossing behavior of the Florida panther. Differences by age and gender were determined, as well as the effect of road size. Results indicate that vehicle collisions are a major threat to the Florida panther population, especially adult males. Major roads present a stronger barrier to movement than minor roads, and the movement of females is more affected than that of males. Road networks in south Florida have essentially segregated the movement of the sexes and have fragmented the limited remaining habitat of the Florida panther.► Florida panther telemetry data from 1981 until 2004 as well as detailed road networks and vegetation maps were used to determine the influence of roads on individual panthers.► Vehicle collisions are a major threat to the Florida panther population, especially adult males.► Major roads form more of a barrier to movement than minor roads, and females are affected more than males.► Roads have essentially segregated the movement of the sexes and have fragmented not only the limited habitat of the Florida panther, but also segments of the adult population critical to the propagation of the species.
Repeatability of street geocoding was characterized in terms of completeness and positional accur... more Repeatability of street geocoding was characterized in terms of completeness and positional accuracy by using different street network datasets to geocode the same address input file. Match rates were highest for local street centrelines followed by StreetMap USA 2005 and TIGER 2000 data. Positional accuracy was highest for local street centrelines, while StreetMap USA 2005 and TIGER 2000 were nearly identical. Rural addresses were geocoded less accurately than urban addresses. Multi-family residential and commercial, institutional or industrial addresses were geocoded less accurately than urban single family residential addresses. The enhancement of TIGER 2000 data by commercial firms resulted in higher match rates but not in improved positional accuracy. The study has also highlighted the unique nature of multi-family and non-residential addresses in terms of the quality of their street geocoded locations. When such addresses are of specific interest alternatives to traditional street geocoding may need to be considered.
The purpose of this study is to determine the effect of vertical accuracy of a Digital Elevation ... more The purpose of this study is to determine the effect of vertical accuracy of a Digital Elevation Model (DEM) on the occurrence of topographic depressions. Stochastic depression modeling of a medium-resolution lidar DEM for a low-relief study area was carried out using Monte Carlo simulation of a range of Root Mean Square Error (RMSE) values for vertical error. Depth and size of observed depressions were compared to the stochastic modeling results in order to separate artificial from real depressions.
The 3G iPhone was the first consumer device to provide a seamless integration of three positionin... more The 3G iPhone was the first consumer device to provide a seamless integration of three positioning technologies: Assisted GPS (A-GPS), WiFi positioning and cellular network positioning. This study presents an evaluation of the accuracy of locations obtained using these three positioning modes on the 3G iPhone. A-GPS locations were validated using surveyed benchmarks and compared to a traditional low-cost GPS receiver running simultaneously. WiFi and cellular positions for indoor locations were validated using high resolution orthophotography. Results indicate that A-GPS locations obtained using the 3G iPhone are much less accurate than those from regular autonomous GPS units (average median error of 8 m for ten 20-minute field tests) but appear sufficient for most Location Based Services (LBS). WiFi locations using the 3G iPhone are much less accurate (median error of 74 m for 58 observations) and fail to meet the published accuracy specifications. Positional errors in WiFi also reveal erratic spatial patterns resulting from the design of the calibration effort underlying the WiFi positioning system. Cellular positioning using the 3G iPhone is the least accurate positioning method (median error of 600 m for 64 observations), consistent with previous studies. Pros and cons of the three positioning technologies are presented in terms of coverage, accuracy and reliability, followed by a discussion of the implications for LBS using the 3G iPhone and similar mobile devices.
International Journal of Industrial Organization, 2009
Theory predicts intense price competition results when firms cluster with rivals. Yet, strong evi... more Theory predicts intense price competition results when firms cluster with rivals. Yet, strong evidence of clustering is found in previous empirical research. Researchers typically measure clustering by comparing observed location patterns to random assignment. The random assignment benchmark does not, however, account for zoning and geography and therefore might overstate the extent of strategic agglomeration. As evidence, we find that public elementary schools cluster more than random, not because of agglomeration economies, but due to demand density and limited location options. We argue that a better measurement of strategic agglomeration is to compare across product markets with similar zoning and other location restrictions but different benefits from agglomeration. We use L-function analysis of five product markets in five cities. We find that retailers with greater ability to differentiate their products are more likely to strategically cluster.
Many spatial analysis techniques rely on the ability to geocode individual locations based on add... more Many spatial analysis techniques rely on the ability to geocode individual locations based on addresses or other descriptive information. The quality of geocoding and its effect on spatial analysis have received some attention in the literature, in particular in the field of health. This article reviews the foundation of geocoding and presents a framework for evaluating geocoding quality. Errors introduced by street gecoding include incompleteness, positional error, and incorrect assignment to geographic units. A review of empirical studies suggests that these errors are neither small nor random in nature and that substantial bias may be introduced in spatial analysis that employs the results of geocoding. Several alternatives have also emerged, including the use of address points and parcels, and these are gradually becoming more widely used. Several areas for future research on geocoding have been identified: (i) refinements of address data models to incorporate complex addressing situations; (ii) development of error propagation techniques to determine the level of geocoding quality required for a particular analysis scenario; (iii) development of measures of reliability for geocoding results; (iv) comparative analysis of geocoding quality across different jurisdictions; and (v) validation of online geocoding services and volunteered geographic information.
The Shuttle Radar Topography Mission (SRTM) was flown in February 2000 and collected the first ev... more The Shuttle Radar Topography Mission (SRTM) was flown in February 2000 and collected the first ever high-resolution near-global digital elevation data. The final SRTM data have become widely available at 1 arc-second resolution for the United States and 3 arc-second resolution for other areas. This article reviews the background of the SRTM mission, the data quality characteristics of the SRTM elevation data, and the many applications of SRTM elevation data that have emerged in recent years, including forest ecology, volcanology, glaciology, geomorphology, and hydrology. SRTM data have been particularly useful for areas where previously limited topographic data were available, but results from STRM data also compare reasonably well with those obtained from other high-resolution digital elevation models.
Python Scripting for ArcGIS is a guide to help experienced users of ArcGIS for Desktop get starte... more Python Scripting for ArcGIS is a guide to help experienced users of ArcGIS for Desktop get started with Python scripting. This book teaches how to write Python code that works with spatial data to automate geoprocessing tasks in ArcGIS. Readers can thus learn the skill set needed to create custom tools. The book contains 14 chapters, with the corresponding data and exercises on the accompanying DVD. A 180-day trial of ArcGIS 10.1 for Desktop software is also provided as an online download. Key topics in this book include: Python language fundamentals, Automating geoprocessing tasks, Exploring and manipulating spatial data, Working with geometries and rasters, Map scripting, Debugging and error handling, Creating functions and classes, and Creating and sharing script tools. More details on the book can be found at the Esri Press website: http://esriurl.com/5564. This includes sample chapters for download. Instructors who are considering the book as a textbook for a course can request a deskcopy from Esri Press: http://esripress.esri.com/offers/deskcopy.
Metropolitan WiFi positioning is widely used to complement GPS on mobile devices. WiFi positionin... more Metropolitan WiFi positioning is widely used to complement GPS on mobile devices. WiFi positioning typically has very fast time-to-first-fix and can provide reliable location information when GPS signals are too weak for a position fix. Several commercial WiFi positioning systems have been developed in recent years and most newer model smart phones have the technology embedded. This study empirically determined the performance of WiFi positioning system on two different mobile devices. Skyhook's system, running on an iPhone and a laptop, was selected for this study. Field work was carried out in three cities at a total of 90 sites. The positional accuracy of WiFi positioning was found to be very similar on the two devices with no statistically significant difference between the two error distributions. This suggests that the replicability of WiFi positioning on different devices is high based on aggregate performance metrics. Median values for positional accuracy in the three study areas ranged from 43 to 92 m. These results are similar to earlier independent evaluations of Skyhook's system. The number of access points (APs) observed on the iPhone was consistently lower than that on the laptop. This lower number of APs, however, was not found to reduce positional accuracy. In general, no relationship was found between the number of APs and positional accuracy for either device, counter to earlier findings. The results indicate, however, that WiFi positioning can be achieved with a small number of APs (5–10), but that increased numbers of APs do not contribute to improved positional accuracy. Despite the agreement in aggregate performance metrics between the two devices, the replicability of WiFi positioning using Skyhook's system in terms of getting the same location by using two different devices at approximately the same place and time was relatively poor. Implications for location-based services on mobile devices are discussed.
Global Positioning System devices are increasingly being used for data collection in many fields.... more Global Positioning System devices are increasingly being used for data collection in many fields. Consumer-grade GPS units without differential correction have a published horizontal positional accuracy of approximately 10–15 m (average positional accuracy). An attractive option for differential correction for these GPS units is the Wide Area Augmentation System (WAAS). Most consumer-grade GPS units on the market are WAAS capable. According to the Federal Aviation Authority (FAA), the WAAS broadcast message provides integrity information about the GPS signal as well as accuracy improvements, which are reported to improve accuracy to 3–5 m. Limited empirical evidence has been published on the accuracy of WAAS-enabled GPS compared to autonomous GPS. An empirical study was conducted comparing the horizontal and vertical accuracy of WAAS-corrected GPS and autonomous GPS under ideal conditions using consumer-grade receivers. Data were collected for 30-min time spans over accurately surveyed control points. Metrics of median, 68th and 95th percentile, Root Mean Squared Error (RMSE), and average positional accuracy in the horizontal and vertical dimensions were computed and statistically compared. No statistically significant difference was found between WAAS and autonomous position fixes when using two different consumer-grade units. When using WAAS, a third unit type exhibited a statistically significant improvement in positional accuracy. Analysis of data collected for a 27-h time span indicates that while WAAS is altering the estimated position of a point compared to an autonomous position estimate, WAAS augmentation actually appears to decrease the positional accuracy.
The Florida panther (Puma concolor coryi) is a relatively well studied species and it is well est... more The Florida panther (Puma concolor coryi) is a relatively well studied species and it is well established that the most important threat to panthers include limited habitat area and continued habitat loss and fragmentation. Despite the recognition that roads result in panther mortality and may limit panther movement there has been very limited research on the importance of roads. In the current study panther telemetry data from 1981 until 2004, detailed road networks and vegetation maps were used to determine vehicle-related mortality and road crossing behavior of the Florida panther. Differences by age and gender were determined, as well as the effect of road size. Results indicate that vehicle collisions are a major threat to the Florida panther population, especially adult males. Major roads present a stronger barrier to movement than minor roads, and the movement of females is more affected than that of males. Road networks in south Florida have essentially segregated the movement of the sexes and have fragmented the limited remaining habitat of the Florida panther.► Florida panther telemetry data from 1981 until 2004 as well as detailed road networks and vegetation maps were used to determine the influence of roads on individual panthers.► Vehicle collisions are a major threat to the Florida panther population, especially adult males.► Major roads form more of a barrier to movement than minor roads, and females are affected more than males.► Roads have essentially segregated the movement of the sexes and have fragmented not only the limited habitat of the Florida panther, but also segments of the adult population critical to the propagation of the species.
Repeatability of street geocoding was characterized in terms of completeness and positional accur... more Repeatability of street geocoding was characterized in terms of completeness and positional accuracy by using different street network datasets to geocode the same address input file. Match rates were highest for local street centrelines followed by StreetMap USA 2005 and TIGER 2000 data. Positional accuracy was highest for local street centrelines, while StreetMap USA 2005 and TIGER 2000 were nearly identical. Rural addresses were geocoded less accurately than urban addresses. Multi-family residential and commercial, institutional or industrial addresses were geocoded less accurately than urban single family residential addresses. The enhancement of TIGER 2000 data by commercial firms resulted in higher match rates but not in improved positional accuracy. The study has also highlighted the unique nature of multi-family and non-residential addresses in terms of the quality of their street geocoded locations. When such addresses are of specific interest alternatives to traditional street geocoding may need to be considered.
The purpose of this study is to determine the effect of vertical accuracy of a Digital Elevation ... more The purpose of this study is to determine the effect of vertical accuracy of a Digital Elevation Model (DEM) on the occurrence of topographic depressions. Stochastic depression modeling of a medium-resolution lidar DEM for a low-relief study area was carried out using Monte Carlo simulation of a range of Root Mean Square Error (RMSE) values for vertical error. Depth and size of observed depressions were compared to the stochastic modeling results in order to separate artificial from real depressions.
The 3G iPhone was the first consumer device to provide a seamless integration of three positionin... more The 3G iPhone was the first consumer device to provide a seamless integration of three positioning technologies: Assisted GPS (A-GPS), WiFi positioning and cellular network positioning. This study presents an evaluation of the accuracy of locations obtained using these three positioning modes on the 3G iPhone. A-GPS locations were validated using surveyed benchmarks and compared to a traditional low-cost GPS receiver running simultaneously. WiFi and cellular positions for indoor locations were validated using high resolution orthophotography. Results indicate that A-GPS locations obtained using the 3G iPhone are much less accurate than those from regular autonomous GPS units (average median error of 8 m for ten 20-minute field tests) but appear sufficient for most Location Based Services (LBS). WiFi locations using the 3G iPhone are much less accurate (median error of 74 m for 58 observations) and fail to meet the published accuracy specifications. Positional errors in WiFi also reveal erratic spatial patterns resulting from the design of the calibration effort underlying the WiFi positioning system. Cellular positioning using the 3G iPhone is the least accurate positioning method (median error of 600 m for 64 observations), consistent with previous studies. Pros and cons of the three positioning technologies are presented in terms of coverage, accuracy and reliability, followed by a discussion of the implications for LBS using the 3G iPhone and similar mobile devices.
International Journal of Industrial Organization, 2009
Theory predicts intense price competition results when firms cluster with rivals. Yet, strong evi... more Theory predicts intense price competition results when firms cluster with rivals. Yet, strong evidence of clustering is found in previous empirical research. Researchers typically measure clustering by comparing observed location patterns to random assignment. The random assignment benchmark does not, however, account for zoning and geography and therefore might overstate the extent of strategic agglomeration. As evidence, we find that public elementary schools cluster more than random, not because of agglomeration economies, but due to demand density and limited location options. We argue that a better measurement of strategic agglomeration is to compare across product markets with similar zoning and other location restrictions but different benefits from agglomeration. We use L-function analysis of five product markets in five cities. We find that retailers with greater ability to differentiate their products are more likely to strategically cluster.
Many spatial analysis techniques rely on the ability to geocode individual locations based on add... more Many spatial analysis techniques rely on the ability to geocode individual locations based on addresses or other descriptive information. The quality of geocoding and its effect on spatial analysis have received some attention in the literature, in particular in the field of health. This article reviews the foundation of geocoding and presents a framework for evaluating geocoding quality. Errors introduced by street gecoding include incompleteness, positional error, and incorrect assignment to geographic units. A review of empirical studies suggests that these errors are neither small nor random in nature and that substantial bias may be introduced in spatial analysis that employs the results of geocoding. Several alternatives have also emerged, including the use of address points and parcels, and these are gradually becoming more widely used. Several areas for future research on geocoding have been identified: (i) refinements of address data models to incorporate complex addressing situations; (ii) development of error propagation techniques to determine the level of geocoding quality required for a particular analysis scenario; (iii) development of measures of reliability for geocoding results; (iv) comparative analysis of geocoding quality across different jurisdictions; and (v) validation of online geocoding services and volunteered geographic information.
The Shuttle Radar Topography Mission (SRTM) was flown in February 2000 and collected the first ev... more The Shuttle Radar Topography Mission (SRTM) was flown in February 2000 and collected the first ever high-resolution near-global digital elevation data. The final SRTM data have become widely available at 1 arc-second resolution for the United States and 3 arc-second resolution for other areas. This article reviews the background of the SRTM mission, the data quality characteristics of the SRTM elevation data, and the many applications of SRTM elevation data that have emerged in recent years, including forest ecology, volcanology, glaciology, geomorphology, and hydrology. SRTM data have been particularly useful for areas where previously limited topographic data were available, but results from STRM data also compare reasonably well with those obtained from other high-resolution digital elevation models.
Spatial data quality is a paramount concern in all GIS applications. Existing spatial data accura... more Spatial data quality is a paramount concern in all GIS applications. Existing spatial data accuracy standards, including the National Standard for Spatial Data Accuracy (NSSDA) used in the United States, commonly assume the positional error of spatial data is normally distributed. This research has characterized the distribution of the positional error in four types of spatial data: GPS locations, street geocoding, TIGER roads, and LIDAR elevation data. The positional error in GPS locations can be approximated with a Rayleigh distribution, the positional error in street geocoding and TIGER roads can be approximated with a log-normal distribution, and the positional error in LIDAR elevation data can be approximated with a normal distribution of the original vertical error values after removal of a small number of outliers. For all four data types considered, however, these solutions are only approximations, and some evidence of non-stationary behavior resulting in lack of normality was observed in all four datasets. Monte-Carlo simulation of the robustness of accuracy statistics revealed that the conventional 100% Root Mean Square Error (RMSE) statistic is not reliable for non-normal distributions. Some degree of data trimming is recommended through the use of 90% and 95% RMSE statistics. Percentiles, however, are not very robust as single positional accuracy statistics. The non-normal distribution of positional errors in spatial data has implications for spatial data accuracy standards and error propagation modeling. Specific recommendations are formulated for revisions of the NSSDA.
3. Joseph PM. Paradoxical ozone associations could be due to methyl nitrite from combustion of me... more 3. Joseph PM. Paradoxical ozone associations could be due to methyl nitrite from combustion of methyl ethers or esters in engine fuels. Environ Int 2007; 33: 1090–106. 4. Joseph PM. A novel hypothesis to explain trafficrelated nocturnal cough. Occup Environ Med 2008; 65: 575.
The correspondence section is a public forum and, as such, is not peer-reviewed. EHP is not respo... more The correspondence section is a public forum and, as such, is not peer-reviewed. EHP is not responsible for the accuracy, currency, or reliability of personal opinion expressed herein; it is the sole responsibility of the authors. EHP neither endorses nor disputes their published commentary.
P. Devereaux Jennings, Paul A. Zandbergen and Martin L. Martens scholarly strategy process resear... more P. Devereaux Jennings, Paul A. Zandbergen and Martin L. Martens scholarly strategy process research goes on, perhaps more than ever, suggesting that there is something fundamental and deeply interesting and profound about how strategies are made, where they originate, and how the process of strategy-making impacts the performance of organizations.(szulanski, Porac et al., 2005: xv)
Social and ecological systems must be more tightly coupled if the health of the biosphere is to b... more Social and ecological systems must be more tightly coupled if the health of the biosphere is to be improved. So goes the argument of several well-known ecological thinkers and activist organizations (Laszlo and others, 1977; Daly and Cobb, 1994; Gladwin, 1992; Meadows, 1992; Suzuki, 1997). Broadly speaking, this normative position also has theoretical and empirical support from organization theory, particularly from the institutional perspective (Friedland and Alford, 1991; Jepperson, 1991; Meyer and Scott, 1983).
The goal of this research program was to establish stronger quantitative relationships between hu... more The goal of this research program was to establish stronger quantitative relationships between human activities and practices in an urban watershed and the quality of the aquatic ecosystem so that proactive management programs could be developed to ameliorate the negative effects of the human activities.
EXECUTIVE SUMMARY The purpose of the current research was to contribute to the improved robustnes... more EXECUTIVE SUMMARY The purpose of the current research was to contribute to the improved robustness of predictive crime mapping techniques. Our goal was to investigate the effect of data quality on predictive hotspot mapping analysis in order to achieve the following three objectives:
• Development of an analysis methodology for housing affordability at the level of individual hou... more • Development of an analysis methodology for housing affordability at the level of individual housing units, calibrated using selected field observations for rental properties;• Application of the methodology to all of Miami-Dade County to generate statistical and cartographic summaries of the availability and spatial distribution of affordable housing in Miami-Dade County;
Abstract: Training and education of all stakeholders involved in the process of watershed managem... more Abstract: Training and education of all stakeholders involved in the process of watershed management can contribute to it's effective implementation. Recent advances in distance education technologies have created new and promising opportunities for making training available to a wider audience.
Abstract—Error propagation modeling for terrain analysis can provide insights into the robustness... more Abstract—Error propagation modeling for terrain analysis can provide insights into the robustness of terrain derivatives. For unconstrained terrain derivatives, such as stream and watershed delineation, the most widely used technique for error propagation modeling employs a Monte Carlo simulation of a spatially autocorrelated error model.
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