The location of Outpost 7
Outpost 7 was an outpost constructed on an asteroid by Starfleet in 2160. This outpost was one of seven Earth Outpost Stations located in Sector Z-6 on the Federation side of the Romulan Neutral Zone.
During the Neutral Zone Incursion of 2266, the location of Outpost 7 was labeled on a map of Sector Z-6 that was displayed on the bridge viewscreen of the USS Enterprise during the Neutral Zone Incursion. (TOS: "Balance of Terror", production art)
In 2366, this outpost received a warning from Starfleet Command about an alleged Romulan base on Nelvana III. (TNG: "The Defector")
According to the Star Trek: Star Charts (pg. 66), there were 23 Earth outposts. Outposts 1 to 8 were mentioned in dialogue or were seen on the Z-6 Sector map in "Balance of Terror" and Outpost 23 was mentioned in dialogue in "Future Imperfect". Outpost 7 was constructed in an area of space that been contested over during the Romulan War Theater of Operations (2156-2160).