The Washington Post is also helping us understand the spread of ISIS. This time a bit more interactively than we have seen from the Times. This is a step-by-step (ish) explanation. Though, I quibble with the decision to link cities by dotted lines. That can create the illusion that ISIS fighters moved directly from city to city when I highly doubt they took that exact path.
Credit for the piece goes to Swati Sharma, Laris Karklis, and Gene Thorp.