Sector One encompasses a significant portion of the eastern UK, covering areas from London in the south, all the way to Edinburgh in the north. Initially, the sector included all roads located between the A1 and A2. However, to better define the southern edge of this sector, the boundary was moved from the A2 to the River Thames. This adjustment resulted in a more geographically cohesive sector, providing a clear demarcation between the sector's roads and those lying further south of the Thames.