Internet access to different servers facilitates the acquisition of professional recently updated databases. Access to several state and national clearinghouses by researchers, health professionals, students, general public, etc. allows the download of usually free databases, although these may be not as up to date as those purchased from private companies. Some clearinghouses, with or without restrictions, can be found on web pages maintained by government agencies such as the Environmental Protection Agency, the United States Geological Survey, some state Departments of Natural Resources, and different universities in the United States. The information usually can be downloaded in Arc/Info export format and is increasingly being made available in the shapefile format for ArcView.

What makes GIS unique is its capacity as a decision support system by integrating spatially referenced data (Cowen 1988). It produces maps that portray present and predict future situations based on the information available. These visual maps greatly simplify the health professional’s work when confronted with several multiple sources which at first may seem not to have a defined relationship. GIS is an important factor in public health studies dealing with health assessments, disease surveillance, environmental risk, site assessments, air, water and soil pollution prevention, among others. Public health research studies have been developed in different countries using GIS. For example, a malaria transmission dynamics study in India found that malaria annual parasite incidence showed a relationship with water table, soil type, irrigation and water quality (Sharma et. al. 1997), maps have identified areas at risk for groundwater pollution in an area of Italy (Riparbelli et. al. 1996) and population exposure to air pollution concentrations of SO2 has been mapped in Poland (Gorynsky et. al. 1997). These and other studies use the advanced functionality of network analyst or the spatial analysis of GIS, where the software can be queried to generate information on a specific location, or the accessibility by admission rates to a hospital by children with malaria (Schellenberg JA et. al. 1998), or the area of influence of a chemical plant’s contaminant plume on the local population based on census data.

The Global Positioning System (GPS) is based on coordinate measurements with the help of several satellites in orbit around the earth. A hand-held satellite navigation system is utilized to find the accurate positional data of the coordinates of a location by presenting a latitude and longitude unique to each object measured. Satellites on semi-synchronous orbit receive a signal from the GPS device and bounce it back to the system. This small device receives the signal from three different satellites. It then calculates differences between the sent signal and the received signal, obtaining the latitude and longitude of the location. Even though the signal processed is degraded for civilian use by the Department of Defense to be less accurate, through Diferential GPS accuracy can be incremented (Larijani 1998). This enriches the quality of spatial and non-spatial data for analysis as it can then be geocoded by assigning coordinates to each entity. It increases the precision of generated maps. The wealth and accuracy of data from GPS enriches GIS databases (Larijani 1998).

In the case of Phase I environmental site assessments (ESAs), the use of GIS is very important. It enables us to depict the information in an portable electronic format, thus facilitating map understanding. ESAs are performed as a measure to reduce environmental liabilities or as a way to focus on current environmental conditions. To create layouts of a commercial or industrial study site we can use a number of databases and maps. The information for a specific site can be found in databases at national, state and local level. At national level we can use regulatory agency listings such as the National Priority List or Superfund list, the Comprehensive Environmental Response, Compensation, and Liability Act Information System (CERCLIS), the Resource Conservation and Recovery Act (RCRA) for treatment, storage and disposal facilities and large and small quantity generators. Some databases may be found on the World Wide Web through the EPA Geographic Information Query system and the EPA Regulated Facilities Query Database. At state level we can access information from the appropriate health departments, Bureaus of Water and Departments of Natural Resources to retrieve information regarding underground and aboveground storage tanks, leaking underground storage tanks, state landfills and solid waste disposal sites. Additional databases which can be accessed are those gathered by the Emergency Response Notification System (ERNS) and the Toxic Release Inventory System (TRIS). All databases have to be previously checked for accuracy before they are utilized.

Digitized mapping is also important in the health field. Several web pages may provide geographic data such as Digital Elevation Models (DEM), topographic, wetland, water quality, soil, hydrology and land use/land cover maps in the form of boundary files, roads, locations, landmarks, etc. These are added as themes to the project. Additionally aerial photography is important in observing historical changes in the landscape over the years as there could be an underlying health related problem not observable on site at the time of the study such as an old covered landfill or an abandoned underground storage tank. The attribute databases (demographics, specific industrial data, etc) will be appropriately joined through common fields. The GIS software will be queried for specific information relative to the study and the integration will be used to produce layouts. The proximity of small and large quantity generators of wastes, radii of influence from nearby underground storage tanks and Superfund sites are of great interest when producing different overlays of the site through spatial analyst. This also permits us to focus on nearby watershed and wetlands characteristics and the interaction with storage tanks in the vicinity. Final maps may define what problems may arise or may be present and corrective actions may have to be taken in order to lessen the environmental liability of the site. This is one of multiple topics where GIS can contribute to generate maps leading to solutions in all areas of public health.

Studies where GIS can be applied have expanded from those of purely geographical nature. Other areas where the utility of GIS has been demonstrated are in exposure assessments, community-based mapping, remote sensing, infectious disease case studies, environmental risk factors, chronic diseases, birth defects studies, demography and community health, environmental justice, modeling and statistical analysis, health protection, etc. The facilitation of information and databases through the World Wide Web is important for scientists, researchers, public health professionals in general and ultimately the public, to whom most of the information is geared to once it is analyzed. It is also important that information exchange take place between professionals in order to promote idea sharing and decision making through multiple channels at local, state, national and international levels.

1. Becker KM; Glass GE; Brathwaite W; Zenilman JM (1998) Geographic epidemiology of gonorrhea in Baltimore, Maryland, using a geographic information system. Am J Epidemiol, Apr 1 147(7):709-16
2. Clarke KC; McLafferty SL; Tempalski BJ (1996) On epidemiology and geographic information systems: a review and discussion of future directions. Emerg Infect Dis, Apr-Jun 2(2):85-92
3. Cowen DJ (1988) GIS versus CAD versus DBMS: what are the differences?. Photogrammetric Engineering and Remote sensing, Nov. Vol 54, No. 11, pp. 1551-1555
4. Cowen DJ, (1994) The Importance of GIS for the average person. GIS in government. The Federal Perspective, pp. 7-11.
5. DeMers MN (1997) Fundamentals of Geographic Information Systems. John Wiley & Sons Inc.
6. Gatrell AC; Bailey TC Interactive spatial data analysis in medical geography. Soc Sci Med, 42(6):843-55 1996 Mar
7. Gory´nski P; Szutowicz I; Wojtyniak B (1997) The assessment of population exposure to atmospheric air pollution Rocz Panstw Zakl Hig, 48(1):37-46
8. Hightower AW; Klein RE (1995) Building a geographic information system (GIS) public health infrastructure for research and control of tropical diseases Emerg Infect Dis, Oct-Dec 1(4):156-7
9. Hightower AW; Ombok M; Otieno R; Odhiambo R; Oloo AJ; Lal AA; Nahlen BL; Hawley WA (1998) A geographic information system applied to a malaria field study in western Kenya. Am J Trop Med Hyg, Mar 58(3):266-72
10. Jacquez GM (1995) The map comparison problem: tests for the overlap of geographic boundaries. Stat Med, Nov 15-30 14(21-22):2343-61
11. Larijani LC (1998) GPS for everyone: how the global positioning system can work for you. American Interface Corporation, N. Y.
12. Pavlov SV; Vasilev AN; Leontev AV (1997) Geographical informational technology as the basis for the informational integration for the large-scale evaluation of the environment Med Tr Prom Ekol, (12):25-7
13. Riparbelli C; Ferioli A; Azimonti G; Regidore C; Battipede G; Maroni M (1996)Impact of pesticides to groundwater resources in an alluvial plain using a geographical information system. Cent Eur J Public Health, Feb 4 (1):21-4
14. Schellenberg JA; Newell JN; Snow RW; Mungala V; Marsh K; Smith PG; Hayes RJ (1998)An analysis of the geographical distribution of severe malaria in children in Kilifi District, Kenya. Int J Epidemiol, Apr 27(2):323-9
15. Sharma VP; Srivastava A (1997) Role of geographic information system in malaria control. Indian J Med Res, Aug 106:198-204
16. Vine MF; Degnan D; Hanchette C (1997) Geographic information systems: their use in environmental epidemiologic research. Environ Health Perspect, Jun 105(6):598-605