I just finished checking out the map. I'll just split it up into pros and cons so I can give concise feedback.

Pros:

There is good theme on the map. It pulls of that abandoned feel with a hint of apocalyptic cause in there.

The map was fun to traverse. There were plenty of hidden paths, fun jumps and stunts or just eye catching scenes.

I like the green fog that blankets the map. It makes the map feel larger and fits in with your backstory.

Nice use of multiple layers to add texture and depth to things. I also like the use of the alien bugs on the map. Very clever.

Cons:

Certain areas felt too empty or incomplete. The Pelican platform is a good example. I can understand a Pelican needs space but in infection, that's a huge handicap for the zombies. Additionally, add more value to the road/cars. With that many of the same colored van just stacked up in one place, it appears a bit lazy. Mix it up, it's a nice touch on the map, give it some attention.

Clear blue sky clashes with on map environment. Pretty self explanatory but it caught my eye and broke the immersion a bit.

I'm eager to see where you take the map. It has potential and you did a nice job with what you have now.