Will I be expected to know all the answers at interview?

In a word: no. The key thing to remember about an interview at Oxford or Cambridge is that the tutors are not looking for someone who knows the answers already, they're looking for someone they really want to teach. The questions they ask of you, whether they're based on a map, or graph, or chart which they will give you to look at, are designed to be quite difficult. You might have some familiarity that will get you started, but they want to see how you think. They want to see if you can make swift and logical arguments on your feet to reach a plausible conclusion.By way of an example, in one of my interviews I was presented with a map of water stress in the USA, and asked to describe and then explain the patterns I could see. I offered one explanation, and was given another graph which proved me wrong, and asked to suggest another, alternative, explanation. This happened several times, with me using the available evidence to reach a reasonable conclusion, being disproved, and having to work to the next possible explanation. It wasn't easy, but I actually quite enjoyed the exercise.