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Phthalates

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Janet Gray, Ph.D.
Janet Gray, Ph.D.

As author of our 2008 and 2010 State of the Evidence reports, Dr. Gray drives the science behind all our work.

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Geographic Information Systems (GIS) Mapping

Overview

Definition: The analysis and visual display of spatial relationships and environmental, demographic, historical and health-related data using geographical maps.

Classification: Tool and technique for human study

In addition to their important use in larger health-tracking programs, Geographic Information Systems (GIS) provide an important technology for examining the relationships between multiple factors within smaller geographically defined areas. GIS studies allow for the complex spatial mapping of many environmental, demographic, historical and health-related variables, including those reported at the individual level. These studies result in detailed individual and community information that can be used to evaluate relationships among exposures that occur differently across time and geographic space with later development of diseases, including breast cancer (Graves, 2008).

Examples

Scientists at the Silent Spring Institute in Massachusetts are using GIS mapping to overlay extensive historical exposure records, local chemical contamination profiles, and detailed questionnaire information about chemical usage and personal health histories on Cape Cod. This has led to the creation of the Cape Cod Breast Cancer and Environment Atlas, and to the publication of a number of studies exploring these complex relationships (Brody, 2004; McKelvey, 2004; Rudel, 2003).

Another example of the use of GIS is a study examining disparities in survival rates among women living with breast cancer in association with demographic factors (race/ethnicity and socio-economic status) along with profiles of tumor grades, medical treatment and screening histories. Several clusters of longer or shorter than expected survival ages were identified (e.g., a cluster of shorter than expected survival in the Detroit metropolitan area). The findings of this study suggested a starting point for looking at environmental and other factors that might be influencing mortality rates in these areas (Schootman, 2008).

A new web-based interactive GIS system has been used to demonstrate the capacity of existing technology to allow for scientists and policy makers to create and share spatial maps of disease and environmental exposure distributions (Gao, 2008). While breast cancer is not yet integrated into this system, the technological infrastructure of this project could be applied to breast cancer in the future. At an even more interactive level, and directly relevant to our understanding of issues related to breast cancer, the Harris (Texas) County Breast Portal and Project Safety Net has developed an interactive web-based GIS system (Highfield, 2011) that allows scientists and interested citizens to participate in real-time data entry and analysis, providing a dynamic and flexible tool for addressing ongoing changes in breast cancer rates and profiles in subareas within the target area, as well as social and economic demographics, and availability of different types of medical services for women diagnosed with breast cancer (the focus of this particular project).

Strengths

Use of GIS allows for rigorous quantitative analyses of multiple geographic factors along with more traditional census-based and questionnaire data. GIS allows for storage of large quantities of data and reevaluation when new data is available or when new questions arise. And the software permits researchers to present complex data in dynamic and color-coded displays that clarify main trends from the various analyses being conducted (Aneja, 2011).

Limitations

The accuracy and therefore level of understanding of data obtained with GIS technologies are limited by the resolution of the GIS software that may vary by place and system. When large area maps or datasets are used to study relationships between ecological variables and health outcomes, conclusions can be drawn only about the larger community, not the individual. It is rare to have such high-resolution data to study specific homes or neighborhoods. GIS allows researchers to observe overlapping patterns of exposures and disease, but it cannot determine whether exposures actually caused the diseases. Finally, many GIS studies do not account for historical changes in the environment or the great mobility of people across geographic lines, both during a normal day/week or across years (Aneja, 2011).