Data is sourced from the Pennsylvania Department of Environmental Protection. Map is designed to illustrate which counties in Pennsylvania have experienced the highest amount of oil and natural gas drilling activity through the calculation of the density of wells drilled per 100 square miles. Data is provided as one record for each well drilled.
Records of wells drilled beginning in 2005 are joined to county areas and then calculated to provide a density figure. The color gradient of dark red depicts counties with the highest concentrations of drilled wells over the chosen time period. The year 2005 is used as a baseline as this period represents the beginning of widespread natural gas drilling in the Marcellus shale formation which underscores much of Pennsylvania.