First Advisor

Jiunn-Der (Geoffrey) Duh

Date of Award


Document Type


Degree Name

Master of Science (M.S.) in Geography




Geographical information systems, Environmental health -- Oregon -- Portland -- Social aspects




This project compares three GIS techniques that estimate populations who are potentially affected by environmental contamination in Portland, Oregon. All three GIS techniques utilize polygon containment to estimate populations potentially exposed to pollutants based on block level census data. In this study, multiple buffer distances at half-mile increments were used across all three techniques. Circular Euclidean distance buffers surrounding a known contaminated property, such as documented brownfields, approximate the contamination zone. Accurate estimates for populations exposed to harmful environmental conditions could provide a better understanding of environmental justice issues. The specific research questions were: 1) Are the population estimates sensitive to the GIS techniques used? 2) Are higher proportions of minority populations closer to brownfields than the general population? The three population estimation techniques are: the centroid containment method, areal apportionment method, and vector-based dasymetric mapping. Centroid containment method assigns the population of a census enumeration unit to its centroid. If the centroid falls within the contamination zone, then the total population of the census unit is counted as being exposed to the pollutant. Areal apportionment method estimates exposed populations by calculating the population based on its proportional size for the area of the census enumeration unit that falls within the contamination zone. Vector-based dasymetric mapping redistributes the population into areas that correspond more directly to resident populations within a census enumeration unit. Building volumes are used to dis-aggregate the census enumeration blocks into smaller spatial units that account for three-dimensional space and more realistically resemble the populations who may reside in the exposure zones. Using the population estimates derived from these methods, I examined if minority populations were disproportionately distributed near brownfields. For question 1, I compared the population estimates from the three methods at various buffer distances to ascertain the reliability of each of their calculations. After the sensitivity analysis was performed, I used a half-mile radius around brownfields as the potential risk area and compared the percentage of minorities in the risk area to the percentage of the total population in the risk area for each of the three GIS techniques. The results indicate all three techniques produced comparable population estimates across the various distance intervals. Consequently, this allowed for a fair comparison across all three GIS methods. In terms of environmental justice the results reported all three estimation techniques to have similar results. As the techniques got more advance, the results showed less inequality for minorities; however, the margin for this difference was only one to two sites depending on which methods are being compared. Also, the vector-based dasymetric method presented a lower percentage of minorities in the risk area when compared to the other two methods, because dasymetric mapping is designed to estimate were people are more likely concentrated. The research from this project presented how GIS could be used to investigate environmental justice, and how different spatial analysis methods could result in uncertainty with population distribution.


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A research paper submitted in partial fulfillment of the requirements for the degree of Master of Science in Geography

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