Shapefiles containing the geographical representation of the Primary Substation Boundaries for SEPD & SHEPD. The primary substation areas are formed from Voronoi polygons based off the point locations of all the secondary substations fed by a given primary substation. This means that every point in a polygon is closest geographically to the assigned secondary substation. The secondary substation polygons are then dissolved with respect to the primary they are connected to form the primary supply areas.