In this report, the National Alliance collected public school enrollment data for the 2014-15 school year to identify communities across the country where the highest proportions of students were enrolled in charter public schools. To calculate these proportions, charter schools were mapped to public school districts based on their address and the school district boundaries. This report compares the enrollment of charter public schools located in traditional school district boundaries with district- run public school enrollment in the same districts, resulting in the enrollment share of charter public schools. It is important to note that students sometimes leave the geographic boundaries of the school district in which they live to attend charter schools. However, the comparison between charter public schools and district-run public schools serves as a proxy for where students who are enrolled in charter public schools would likely have enrolled if those schools were not available.