One of my sources of information (and a great time-waster) is the reddit The Silphroad. Today they published an analysis on boundaries and causes of electric biomes in Pokemon GO. In order to better understand the analysis, here is some background.
What are S2 Cells?
S2 cells are a very clever way to represent a region or a point on a sphere (e.g. the Earth) into a single number. S2 Cells use Hilbert Curves to approximate any point (or better squares) in a bigger square.