The bulk of the data comes from the Metric Geometry and Gerrymandering Group. The cartographic boundaries for the 2019 district redraw comes from the NC Legislature.
Of course, each district is composed of a number of precincts which have remained stable throughout the 2000s. Each precinct is shaded according to the perecentage of Democratic vs Republican votes in that precinct taking into account all Presidential, Gubernatorial, and US Senate races since 2008. Thus, we can get a sense of how "Blue" or "Red" each district leans. More precisely, we can average all of these for each district to get an estimate of the partisan lean of each district.
Taking that a step further, we can measure the degree to which gerrymandering has occurred using the so-called efficiency gap associated with the drawn districts. The most recently redrawn districts have an efficiency gap of 7% - just barely within acceptable levels.