I think it sounds a bit redundant, but it's not incorrect at all. Something like "The field of health geography is often overlooked, but it constitutes a huge area of need in the two fields it entails." or "The field of health geography is often overlooked, but it constitutes a huge area of need in healthcare around the world." might be more concise.

To my ears, it doesn't sound redundant. It expands on the meaning of health geography.

Thank you.

I like to use " although " instead of " but " .. You can also say " huge area of need for both geography and healthcare.