Is this sentence grammatically correct, and what should I do to fix it?

This is probably a really simple question that I probably used to know the answer to, but I do not know anymore.

I have the following, rather long sentence: “Places with undifferentiated highlands always have a high physiological density, while places with humid low-latitude climate almost always have at least a medium density.”

In my opinion, that sentence sounds weird and incorrect, but I am not sure how to fix it. What is wrong with it and what do I do to fix it?