Question about maintaining altitude over varying terrain.

I am going to buy my first drone but I'm still researching the technology. I live in New Mexico where there is ample open, non-restricted space to fly, but the terrain can vary by as much as 600 feet over a quarter mile. My question is, do drones maintain altitude based on the location of take-off and/or the location of the remote, or would it try to maintain "height above ground" and suddenly dip into a canyon if it flew over one? If it helps, the two I am thinking of purchasing is the Mavic 2 Zoom, and the Autel Robotics EVO 4K.Thanks. via /r/drones https://ift.tt/2ZmYsoy