The DTM model I just finished was 15 GB total. It is essentially what the ground would look like if all structures and vegetation like trees or bushes were removed. It is just the terrain with nothing else.
I was out and about yesterday and at a stop sign waiting for the string of cars to move up one car at a time. I looked over the the side at a strip shopping center. They had a pool business there called Pool Savers. I did a total double take because the L of the sign had been removed.
I guess there is not a lot of demand for a poo saver business but what do I know.