The border between Vulcanian space and the Andorian Empire in 2154.
Andorian space or Andorian territory was the territorial region of space claimed by the Andorian Empire that surrounded the Andorian system. The planet Regulus was located just outside of Andorian space, just beyond the range of Andorian listening stations. (ENT: "Kir'Shara")
The class D planet, named by the Andorians as Weytahn, was located on the frontier between the Vulcan and Andorian systems, and both sides had claimed or attempted to annex the planet since the mid-21st century. (ENT: "Cease Fire")
The Border Incursions were a conflict between the Andorians and the Vulcans that took place along the border of their respective territories in 2112. (ENT: "Cease Fire")
In 2154, Malcolm Reed questioned why Enterprise NX-01 was traveling to Andorian territory, despite Admiral Gardner's orders to head back to Earth. Trip Tucker then explained that they were heading back to Earth after a short detour in order to warn the Andorians of a pending attack. (ENT: "Kir'Shara")
From the perspective of Tellar Prime, the planet Babel was on the far side of Andorian space. This made it necessary for NX-01 to transport Tellarite ambassador Gral to Babel in 2154, as Tellarite ships weren't allowed to travel through Andorian territory. When Gral asked if they had entered Andorian space yet, Archer confirmed that they had a few minutes ago. Gral then recalled the last time he had been there, where he stated he was "on the command deck of one of our cruisers, driving those blue demons back into their territory." (ENT: "Babel One")