What??? It doesn't look even remotely like that. A map of a planetary system looks like the examples
shown here, a series of orbital rings around a central star. Since planets don't hover in place but circle the star in their orbits, the only meaningful way to diagram a planetary system is by showing the orbits, the paths they follow over time. The Neutral Zone map is clearly drawn in the style of a star map, a diagram of different star systems, like
this one or
this one. It's showing a boundary between two interstellar territories, each containing multiple stars.
Besides, as I've already said, if the map were on that kind of a scale that would let you discern individual planets, then the Neutral Zone would have to pass
through the Romulan star system, and that makes no sense. Obviously Romii is meant to be a separate star altogether. Even if it were a binary companion as the
Concordance claimed, then assuming the map is to scale, that would probably put the Neutral Zone much less than a light-year from Romulus. It's presumably just a neighboring star several light-years away, like Alpha Centauri to Sol.
I doubt anybody would use "Star Empire" to mean an empire encompassing the planets of a single star, any more than they'd use "starship" for a strictly interplanetary vessel. It would just be an interplanetary empire. The term "Star Empire" implies an empire that encompasses multiple star systems.