When the T-Rex attacks in Jurassic Park, the area on the other side of the fence has low-growing bushes and trees, as well as the spot where the goat was tied. In fact, the T-Rex is clearly seen walking on the ground. However, Dr. Grant escapes by rappelling down the other side of the concrete wall, which has a 100 ft. drop. How did this drop magically appear? In the wide shot you can even see that there's nowhere for the T-Rex to walk.
It may just be a mistake, but a page on the defunct website jplegacy.org tried to find a justification by suggesting that although the ground is level with the wall in most places, in one spot it drops off into a deep ravine or moat, and that's why the fence tapers off there. An excerpt:
Now, let's look at our film evidence: First we have the initial arrival. We can see here that the fence is quite long. If you look, the fence actually doesn't stretch all the way to the tunnel, instead, it all seems to converge into a small point next the tunnel. This would seemingly be an error-a gratuitous error-if the rex's range stretched all the way to the tunnel and further. This is our first hint that the paddock has a boundary further in.
Here's the picture they give showing where the fence drops off on the left, which would be problematic if the ground was still level there since it seems like the T. Rex could just step over:
Here is the original script, which has a descriptive paragraph that basically seems to support the idea above:
the T-rex starts to nudge the Explorer toward the barrier. Over the barrier, there is a gentle terraced area at one side where the rex emerged from, but the car isn't next to that, it's next to a sharp precipice, representing a fifty or sixty foot drop.
This diagram (source unknown, pulled from comments) shows a plausible arrangement. It's appears to be notated in meters, so "-15,00" matches with "fifty feet".
This is something from the book that was not explained in the movie. (well, there was one throw away line that was easily missed) there is a moat between ground level in the T-rex paddock, and the fence. This exists to discourage the dinos from getting close to the fence.
It is this moat that the car is pushed into. There is a section of the book that deals with Grant trying to figure out how to climb out of this moat with Tim and Lex (the T-rex simply steps over it)
There were only six divisions on the whole island. And each division was separated from the road by a concrete moat.
"You know," Ellie said, "some of these dimensions are enormous. Look at this. This concrete moat is thirty feet wide. That's like a military fortification."
"Absolutely not," Arnold said. "These are expensive animals, Mr. Gennaro. We take very good care of them. We maintain multiple barriers. First, the moats." He pressed a button, and the board lit up with a network of orange bars. "These moats are never less than twelve feet deep, and water-filled. For bigger animals the moats may be thirty feet deep.
The T-Rex snapped several lines of cable when it broke out. But during the scene where it pushed the car off. Grant and Lex are near a gap. That's the security moat to keep the animals in place. But the moat isn't a perfect perimeter, there are parts where the land comes straight up to the fence. That's where the animal escaped.