Researchers at such institutions as the Centers for Disease Control and Prevention (CDC) use incidence maps, which plot where and how people have been infected or exposed to such potentially harmful viruses as the influenza, the Ebola Virus, West Nile Virus, and HIV in order to understand the rate of transmission as related to geography. An incidence map may help scientists figure out the origin of a disease and where and how quickly it is spreading. Global incidence maps are of increasing importance in the fight against potentially harmful biological disasters.