It's a subject I actually discussed with multiple people at several occasions and the FS seems to be very inconsistent... And actually nonsense in this regard.
Many of the systems "in the middle" of the starmap seems to be inhabited by both Vasudan and Terran populations and those systems are very likely to be fronline systems during T-V war. Either the borders of PVE and GTA shifted many times during the T-V war or the colonisation efforts of both sides actually happened during the war, completely ignoring it... Which sounds strange, but that's what many facts seems to suggest.
Some selected systems:
- Deneb: Despite being a neighbour to Vasuda and being heavily colonised by vasudan civilian population, this system house major terran population supporting NTF during early FS2.
- Alpha Centauri: Probably mostly vasudan, but was also point of interest of NTF as evidenced by multiplayer missions.
- Antares: Heavily contested during T-V War and populated by both species for being neighbour to Vasuda and central terran colony worlds as well.
- Betelgeuse: Despite being border system, both GTA and PVN are presumably maintaining presence here and the system is apparently important enough for Terrans to deploy Galatea there. Vasudan presence seems to be also strong. Because Betelgeuse is red supergiant at the very end of her lifespan, habitable planets are unlikely to exist, but the system may be interesting due to it's mineral deposits or scientific value.
- Ribos: Just like Betelgeuse, but probably more populated by both sides due to proximity of Antares. Important enough for GTA to maintain large station [Tombaugh] there.
- Beta Cygni: as above.
- Ikeya: Nothing indicates that this system is important for either side.
- Capella: Heavily populated by 240 millions of terrans and vasudans. Such enormous population is unlikely to migrate there during Reconstruction, so the system is likely to be old colonial world for terrans and vasudans.
- Polaris, Regulus, Sirius, Epsilon Pegasi - Despite proximity to Vasuda, those systems are likely to house mostly terran populations.
- Adhara - Large terran population, and presumably infrastructure. Enough to establish it's own, sovereign state after the fall of GTA.
- Aldebaran - Large vasudan population. Probably the largest after destruction of Vasuda Prime.
- Altair - Minor vasudan population, that likely grew after the Great War due to proximity to new Vasudan capital. This system wasn't explored by either side before the Great War and it's possible, that it was completely unknown earlier.
- Vega - Mixed, but probably mostly vasudan.
- Beta Aquilae - Mixed. Important enough for both sides to be selected as capital of the GTVA.
- Delta Serpentis - Obviously terran.
- Ross 128 - Terran. Important enough to hold at least one large installation [Riviera].
- Laramis and beyond - Confirmed to house infrastructure of numerous, big, terran corporations and one independent state during Reco, so probably mostly terran, but except the distance to core vasudan systems, I see no reason why vasudans would not be able to colonise some of those systems after the Great War.
I guess that almost no system is purely terran or purely vasudan, but majority of them have planets and station inhabited by both instead. Why this happened? I have no idea, but having vasudan neighbour even during T-V war is unlikely to be rare probably since the beginning of the part of history that both species share. I suspect that during the time of FS2, planets in FS may be covered by large patches of lands, owned by Vasudan Empire and regional, terran governments allied under GTVA banner.