In TV and movies featuring attacks on ancient/medieval cities the armies are shown approaching a walled city with nothing outside the city. Is this accurate? Would there have been expanses of empty land around large cities?

Around large cities? I doubt that, unless someone forbade building outside of city walls and was strictly enforcing it. It would be possible in Slavic grods, where you had just few layers of palisade like this: http://static.scholaris.pl/resource-thumb/790/88.jpg or in towns, which were just grounded and didn't really start sprawling.

Let's look at medieval city of Cracow: https://upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Nuremberg_chronicles_-CRACOVIA.png/800px-Nuremberg_chronicles-_CRACOVIA.png

You can see here: Cracow in the middle, town of Casimir on the left, part of the town called Clepardia on the right, royal castle in the background and few monasteries here and there. Both Cracow and Casimir have city walls, because they were populous and important, Clepardia wasn't that important, it had maybe 1000 people, so nobody wanted to invest in building walls there. So in the case of invasion, would invaders just walk in there, start living there and siege city from there? Wrong. Cracow was sieged few times: 1655, 1657, 1772, each time defenders decided to set Clepardia on fire to make it impossible for attackers to use Clepardia as an advantage.