Earth Outpost Station
The Earth Outpost Stations were a series of outposts constructed on asteroids located in Sector Z-6 of the Beta Quadrant, and in neighboring sectors, along the Federation side of the Romulan Neutral Zone. They were established by a treaty after the Earth-Romulan War of the 2160s, which allowed United Earth, and subsequently the Federation, to monitor its side of the Neutral Zone. (; )

In 2259, the location of Outposts Outpost 1 to 7 was labeled on a stellar cartography chart that was seen on the 's ready room viewscreen. () 

Thet same year, the Enterprise and the  assisted the outposts in their retrofitting and brought them supplies. ()

In 2266, four of the eight outposts came under attack from a powerful plasma weapon used by a Romulan Bird-of-Prey; this sneak attack completely destroyed outposts 2, 3, 4, and 8. These outposts had been rebuilt by 2366. (; )

Nearly a century later, a border outpost reported seven Romulan battle cruisers had come within its sensor range – a violation of the Treaty and even a potential prelude to an attack. The outpost sent out a distress call, to which the nearby  responded. Starfleet also requested that the  join the Berlin to project a deterring show of force against the Romulans – which was also a necessary tactical move to ensure that, should a conflict erupt, the Romulans would not have the advantage. Nothing came of this, and the Romulans chose not to engage or even communicate with Starfleet until later that year. ()

In 2366, the location of four of these outposts were labeled on a Starfleet tactical intelligence analysis map. ()

By 2367, the Neutral Zone outposts had expanded in number, possibly to as many as twenty-three (see Outpost 23). Additional outposts in the region included Outpost Sierra VI. ()

Background information 
The revised final draft script of "Balance of Terror" requested that Earth Outposts 1 to 11 be shown in a star chart which appears in that installment, though only Outposts 1 to 7 are shown in the final version of that display.

While Earth Outpost 23 does not appear in the star chart, there may have been up to twenty-three Earth Outposts established along the Romulan Neutral Zone by 2160. (Star Trek: Star Charts, p. 66)

An okudagram map seen in Starlog Press publication  depicted a portion of the Romulan Neutral Zone. On the map, the locations of Outposts 1-7 were depicted in Federation space. Outposts 41 and 42 were depicted in space claimed by the Klingon Empire. 

These stations' quadrant of origin is inferred based on the position of the Nelvana system as seen in the star chart appearing in the  episode . 

fr:Avant-postes terriens
nl:Aarde buitenpoststation
pl:Posterunki Przystrefowe
Romulan Neutral Zone
Outposts