Under certain hydrological parameters, some aquifers are more prone to contamination than other aquifers.  The parameters that are taken into consideration when calculating the vulnerability of aquifers to contamination are: depth to water (factor d), net recharge (factor r), aquifer media (factor a), soil media (factor s), topography (factor t), impact of the vadose zone (factor i), and the hydraulic conductivity (factor c), which together spell out DRASTIC. Furthermore, there is a weighting factor associated with each of the parameters that can range from one to five.  In addition, the lower the numbers for the DRASTIC index after the assessment of the aquifer, than the lower the risk of aquifer contamination in that area.  These seven parameters derive DRASTIC summary index score, which determines which are more prone to contamination than other.  The significance of the DRASTIC summary index score is that it shows areas that are more prone; as a result, the state or local authorities depending on the scale will place necessary measures in place that would prevent or mitigate contamination of the water supply.  
Using GIS, a map was developed for the seven counties (Hillsborough, Polk, Manatee, Hardee, Sarasota, DeSoto, and Charlotte) in Florida, which shows the DRASTIC summary index score for the Floridan Aquifer System, Surficial Aquifer System, and Other Rocks aquifer.  The developed map is a combination of multiple layers that are stacked on top of each other as shown in Figure 1.