lostisland

There is a major problem with any four player map, and that certain spawn positions will favor specific races in a given matchup. In your map, imagine a Zerg player spawning BR, and a Terran player spawning TR. The Terran has a must easier time harassing the Zerg, because the Zerg will expand away from their opponent, making it hard for them to defend their bases effectively, with less effort from the Terran. On the other hand, if it was Zerg TL and Terran TR, this is a bit more defensible. Though the inclusion of the center-based diagonal base makes defending in rotational imbalanced situations easier, I worry that it might not be enough, and players might still opt to take it as the fourth instead, due to three paths intersecting it. This is effectively the reason 4 player maps are avoided, so this map might be best saved for a future time.
The map beyond its bases feels like a bunch of narrow hallways, while perhaps not too narrow, it doesn't feel like theres much variation. Utilizing some brood-war esque ramps (such as Bloody Ridge) or LOS blockers might help here.
You're missing an unbuildable plate at the bottom of your main ramp.
Zergs cannot walloff with 3 structures at the natural.