It is perfectly simple: you just have to imagine that Canterbury was not there and you were going to build it.
"Let's have a city of at least 40,000 people, and about another 100,000 just outside, with a big tourist attraction in the middle; say, two million visitors a year. We'd better have a university - everyone else has got one - so put 20,000 kids up there. Stick all the well-known stores in the High Street and a couple of supermarkets on the fringe. We'll need a railway station - make that two - a bus station and a coach park. Fire brigade here, police there. Dot some industry around, some churches and a few schools and that should do it."
"What about a hospital?"
"Oh, stick that fifteen miles away."