Public health authorities increasingly wield a simple yet effective tool when they want to track the spread of disease, sway policymakers or gauge the wellness of a given community: the simple map.

Make that a digital map. Government agencies have been using geographic information systems (GIS)"which allows policymakers to get a better handle on health trends by displaying and managing location-based data"for at least a decade. Today, health-related GIS have evolved to the point where there's even a publication devoted to it: The International Journal of Health Geographics.

The pace of GIS adoption in the public-health sphere continues to accelerate. Dr. Georges Benjamin, executive director of the American Public Health Association, suggested that a wealth of GIS applications will follow already established uses of the technology, such as infectious-disease tracking.

"As we begin looking at broader data sets and the ease in which we can do things like compare counties and states for overall healthiness, we will see an explosion in the utilization of these systems," he said.

Benjamin said he believes GIS growth will continue over the next five years.

A number of factors promise to spur that expansion: The wide availability of lowcost or no-cost mapping software such as Google Earth puts GIS in the hands of more people, he said. The greater openness of data is another important force. Open content efforts such as OpenStreet- Map makes GIS data available without the attached strings of usage limitations. The Department of Health & Human Services, meanwhile, has pledged to serve up more of its data, which could find its way into GIS applications.

More data means richer health GIS applications, as more layers of data populate maps. It also means public health officials will need to spend more time combing and managing the expected torrent of new data.

"We need to add this dimensionality, combining multiple elements on the same map," said Julia Gunn, director of the Boston Public Health Commission's Communicable Disease Control Division. "But you don't want a map to get too crowded and lose the story that the data is trying to tell. You're looking for the elegant message that is intuitive to people."

Maps emerge

Indeed, public health authorities cite the intuitive appeal of maps as a key factor behind their adoption. The Boston Public Health Commission, an independent public health agency and the country's oldest health department, uses GIS to track communicable disease rates within neighborhoods. During the height of the H1N1 outbreak in 2009, the commission frequently generated maps of flu activity in sections of Boston.

GIS provided a "visual understanding" of the disease's movement that other forms of data display couldn't produce, Gunn said. "If you're looking just at bar charts or line graphs, you really don't get a sense of the velocity of the disease and how quickly something can be evolving," she said.

Mapping disease rates by neighborhood, and factoring in demographic data, helped the commission craft its response to the flu. In one example, it found an uptick in flu within a neighborhood with a sizable Vietnamese population, Gunn noted. The commission was able to create risk communications messages tailored to that community, she said. The flu mapping effort also helped prioritize the H1N1 vaccine supply.

The combination of geographic and population data "allows you to tailor how you are going to shift resources or do outreach," Gunn explained.

While maps can drive existing health programs, they can also help get others off the ground. That was the case in Philadelphia, where GIS helped spark an initiative to improve community access to healthy food. In 2004, the city-commissioned Food Marketing Task Force released a report recommending the development of more supermarkets in underserved areas of Philadelphia.

Amy Hillier, a graduate student at the time and now assistant professor in city and regional planning with the University of Pennsylvania's School of Design, created a GIS map using ESRI's ArcGIS software to highlight the food deficit. Her maps relied on a data from TradeDimensions that included storage location, size and sales volume together with data from the U.S. Census and Philadelphia Health Department. The map illustrated the connection between poverty, deaths from diet-related diseases, and a lack of food stores.

In light of the task force's work, the Pennsylvania legislature passed the Pennsylvania Fresh Food Financing Initiative, a grant and loan program for building and renovating of supermarkets. Maps helped convince legislators of the need for more stores.

"Maps were not the only part of the argument, but they were an important part," Hillier said. "The maps resonate."

The "˜built environment'

The Philadelphia project, which the Obama administration hopes to apply on a national scale, exemplifies an emerging use case for GIS: assessing what urban planners refer to as the "built environment" and its impact on public health. The built environment includes the human-made elements of the environment: houses, office buildings, and grocery stores, for example.

The Boston Public Health Commission also uses GIS to examine the built environment. The commission publishes the annual Health of Boston report, which provides a snapshot of the health of city residents. The 2010 edition emphasizes the social determinants of health, which includes the physical setting and neighborhood conditions.

Dr. Snehal Shah, director of research and evaluation at the commission and contributor to the Health of Boston report, said GIS helps identify a community's assets: green spaces, bike paths and the presence of food stores and farmer's markets. The ability to provide a better description of the built environment"and linking that portrayal to health outcomes" provides a new perspective on community health, she said.

"We can look at things in a way we weren't able to look at them before," Shah said.

King County, Wash., which includes metropolitan Seattle, also uses GIS to map the built environment. The county taps GIS to create a series of neighborhood walking maps, highlighting trails and businesses within walking or biking range, noted Dennis Higgins, GIS client services manager for King County's GIS Center. The center provides GIS support to King County agencies, including Seattle & King County Public Health.

Another GIS application helps the health department's Environmental Health division manage reviews of businesses holding state permits to handle hazardous materials. The application shows the locations of permit holders and tracks them according to category" permit holders can range from dry cleaners to body shops"and urgency and frequency of review.

"We are producing maps of different regions of the county for each of the field reviewers," Higgins said. The maps are available in hardcopy and in electronic form. The latter can be loaded on a reviewer's laptop.

Open mapping
Such GIS applications may become even more plentiful in the future as mapping tools and datasets become more readily available. Free and open technologies and data have already had an impact in Haiti, where the medical community's response to the January 2010 earthquake included ad-hoc GIS components.

Dr. Jacqueline Burkholder, a public health scientist with the Division of Emergency Operations at the Centers for Disease Control and Prevention [tk], said responders used Google Earth and OpenStreetMap, for example. Google Earth is available for free. The system is p