: Looks like they're visualizing some elements from the original books, as well
: as adding a little backstory to the Prophets "discovering"
: earth. Seems like they didn't even know it was "earth".

In the books, the Prophets knew that Earth was the human homeworld, but they didn't know where it was. The presence of Humanity on Earth was a shock to them, so they clearly didn't think that our homeworld and their target were the same thing. This was made pretty clear at the end of Outskirts...

It's being spoonfed a little to us now, but the map that led them here is something that removes some of the general vagueness surrounding events in the plot... Hope there's a terminal that bridges chief's actions between 2 and 3...