Invited commentary: on the road to improved exposure assessment using geographic information systems.

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Abstract
The use of geographic information is becoming more commonplace in epidemiologic research. Epidemiologists use geographic information systems (GIS) for both designing studies and analyzing data. For example, GIS are used in disease mapping (1–5), identifying potential populations for study (6), conducting small-area analyses of disease rates (7), and undertaking disease cluster and surveillance activities (8–12). Exposure assessors use GIS for developing high-resolution estimates of environmental exposures through data analysis and modeling, for example, for air pollutants (13), pesticides (14–16), and water pollutants (17). Such applications require the consideration of issues that span the disciplines of geospatial science, environmental science, and epidemiology (18). Geospatial issues include the spatial scale and resolution (positional accuracy) of the exposure and health outcome data. Relevant environmental science issues include the fate and transport of specific contaminants in the environment and the validity of the geographic model used to estimate exposure. Finally, issues that must be considered in the epidemiologic study design and analysis include the evaluation of potential confounders and concurrent exposures to multiple risk factors, the etiologic relevance of the exposure levels and exposure timing, and consideration of the disease latency. The estimation of the errors in the exposure metrics and the effects of exposure misclassification or bias on risk estimates are also important considerations in the interpretation of study findings (19).