All credit to Tene(except for the gif, that's all me)
The colors represent the borders of each district, with the tunnels being a neutral zone. This means you can enter into the tunnels but you can not exit into a different raid district. While this may look insane for some, the ability to go ANYWHERE within these districts during a raid is solely when in combat with someone who is outside the base, and once the combat ends (you kill the other player), you must then return to the base. You can not defend or raid from outside of the district the base is in.
Example:
I am raiding the base behind the Elevator in Industrial (dark blue 2), a base owner comes from the opposite side of industrial and shoots me, I can now approach the person who has shot me and fight him over there, instead of right beside the base. This also means I can fully use all of Industrial (excluding other bases) to fight back. I can approach not only from the main street, but via the streets behind the 2 buildings (left side of industrial in the image provided) to go and fight the base owner there, once I have killed him I must now return to the base to continue the actual raid, since I am no longer in combat
With this change you can now actually fight the guy who has already shot you, or who is part of the base (he is on the doors) without being glued to the front of the base you are raiding.
The defenders/raiders will not be able to leave the raid district once they have entered to defend/raid their base. If they leave the raid district it will count as ending their defense/raid of the base.
For raiding any base in sewers if you enter the ring around sewers(example below) after entering the main sewers area your raid/defense is now over. When raiding, use common sense for how far away you can go from the base, the only exception is to chase down a defender attacking you.
These changes do not apply to Kingdom, PD, or Bank. Kingdom, PD, and Bank raid rules remain the same.