known as the modifiable areal unit problem. For example, New York public health officials worried that cancer clusters and causes would be misidentified after they were forced to post maps showing cancer cases by ZIP code on the internet. Their assertion was that ZIP codes were designed for a purpose unrelated to public health issues, and so use of these arbitrary boundaries might lead to inappropriate groupings and then to incorrect conclusions. Further, when comparing data in different aerial units, the difference in size and population means that comparing totals can hide underlying trends in the data. This issue is particularly prevalent with choropleth maps. To solve this, cartographers often apply some form of normalization, such as cases per 100,000 people. Unfortunately, this practice is not always adhered to and can cause potentially misleading maps. Summary Use of GIS in public health is an application area still in its infancy. Like most new applications, there is a lot of promise, but also a lot of pitfalls that must be avoided along the way. Many researchers and practitioners are concentrating of this effort, hoping that the benefits outweigh the risks and the costs associated with this emerging application area for modern GIS techniques. See also Arbia's law of geography boundary problem Biogeography Cartography Concepts and Techniques in Modern Geography distance decay ecological fallacy geography Geospatial predictive modeling geographic information systems geographic information science modifiable areal unit problem Public health spatial analysis spatial autocorrelation Spatial epidemiology Time geography Tobler's first law of geography Tobler's second law of geography Transportation geography Uncertain geographic context problem Urban geography Waldo Tobler Footnotes External links National Center for Health Statistics GIS and Public Health at Esri Consortium for Public Health Informatics International Journal of Health Geographics Applications of geographic information systems Spatial analysis Health informatics Public health