Geographic Information Systems (GIS)

What is a geographic information system?
A geographic information system (GIS) is a computerized database that can be used to store, analyze, and display data, particularly data associated with locations on a map. It is a powerful tool for research when a combination of geographic information is involved, as in health studies.

What information is used in Silent Spring Institute’s GIS?
Examples of data used in the GIS include:

  • Base map data, such as locations of roads, town boundaries, lakes, and rivers;
  • Land use data, such as the locations of residences, commercial and industrial developments, open space, agriculture, military installations, and airports; and
  • Specific data for health studies incorporating such information as census data, geographic distribution of disease, results of laboratory tests of environmental samples, locations of hazardous waste sites, and areas of known pesticide use.

The data stored in the GIS can be displayed as maps, tables, and charts. Institute researchers can create complex maps by combining multiple layers of data similar to overlaying transparencies. For example, locations of drinking water sources can be layered on land use data and information on groundwater flow to identify areas where land use could potentially affect drinking water. We can use the GIS to study changes over time and apply those analyses to investigate the relationships between environmental factors and cancer incidence.

How has the GIS been used in Silent Spring Institute’s Cape Cod Breast Cancer and Environment Study?
Pesticides have been widely used on Cape Cod for many decades. For the Cape Cod Breast Cancer and Environment Study, Silent Spring Institute researchers located and compiled Cape pesticide data from 1940 to 1990. Efforts were made to include the geographic area sprayed, the time period during which it was sprayed, the type of pesticide that was used, and the active ingredients of that pesticide. Other data—such the location of former cranberry bogs where pesticides would have been used—were re-created using land-use maps from 1951 to 1990. The GIS was used to show the locations and timeframes of chemical pesticide use for each town on the Cape. This information was used to compile a residential history of the Cape Cod Study participants to estimate their exposure to chemicals during the time they spent living on the Cape.

Where does Silent Spring Institute get the information it uses in its GIS?
The data about the Cape’s environment used in the Institute’s research include information from the Cape Cod Commission, Cape municipalities, and MassGIS at the Executive Office of Environmental Affairs, as well as details on private wells, pollution discharge sites, hazardous waste sites, and water distribution pipes and plumes, among other sources.

Can the public gain access to this information?
Yes, but only to aggregate data. Research using the GIS has been reported to the Massachusetts Department of Public Health and published in scientific journals. The findings have also been reported to Cape Cod residents and the press. All analyses presented in public forums use aggregate data; no individual name or personal identifying information is ever published or publicly displayed in the GIS.

Is the GIS and the information it uses of benefit only to breast cancer research?
Silent Spring Institute has collected and organized extensive data about the Cape’s environment that we anticipate will be useful for other studies of health issues on the Cape. For example, the Massachusetts Department of Public Health has used the Silent Spring GIS to investigate a cluster of childhood cancers on the Cape.

I live on the Cape and have breast cancer. Should I be worried that my personal information will be made public in the Institute’s GIS maps?
As part of its study design, Silent Spring Institute stipulated that it would maintain data in accordance with stringent requirements that ensure confidentiality of the individuals involved in the study. No information that can identify individuals or the locations of their households will ever be displayed in publications or viewed at a public forum. The information will also be kept safe from unauthorized computer access. Only selected members of the study team—each of whom is required to keep the information confidential—are allowed electronic access to this data.

I live on the Cape and have breast cancer. How did Silent Spring researchers learn about my disease?
By legal statute, physicians and other health care providers must report cases of certain diseases, known as reportable and notifiable diseases, to health authorities. The specific diseases that must be reported vary by state. In Massachusetts, cancer registries must report new cancer cases to the Massachusetts Cancer Registry in the Massachusetts Department of Public Health. Because our study satisfied the state’s rigorous application and review process, Silent Spring researchers obtained information on possible participants from the Massachusetts Department of Public Health.

In addition to collecting diagnostic information about cancer, the registry collects demographic information such as the address, date of birth, nationality, occupational history, smoking history, and vital status for most cases reported to them. The state maintains these records in order to track rates of diseases and to facilitate studies about diseases in the state. The registry keeps this information strictly confidential. To use these data in its study, Silent Spring Institute agreed to maintain these data in accordance with stringent requirements that ensure confidentiality of all participants.

See how Silent Spring Institute researches answer the question "Are Breast Cancer Rates Higher Because the Cape's Population is Older than the General Population of Massachusetts?".