| Quote #4
The mellow air brought in the feel of imminent autumn almost as distinctly as if she had been in the remotest hamlet. Casterbridge was the complement of the rural life around; not its urban opposite. (9.1)
Casterbridge is a pretty sizable town, but it's not filled with mills and factories. It doesn't feel like a big city because it's surrounded by nature: rural, agricultural land.
| Quote #5
Thus Casterbridge was in most respects but the pole, focus, or nerve-knot of the surrounding country life; differing from the many manufacturing towns which are as foreign bodies set down, like boulders on a plain, in a green world with which they have nothing in common. (9.26)
Casterbridge is connected to the surrounding country as strongly as the "nerve-knot," or brain, is connected to the body. It's not like the industrial cities up north, which share nothing with the countryside around them.
| Quote #6
Casterbridge, as has been hinted, was a place deposited in the block upon a corn-field. There was no suburb in the modern sense, or transitional intermixture of town and down. It stood, with regard to the wide fertile land adjoining, clean-cut and distinct, like a chess-board on a green table-cloth. (14.29)
Although Casterbridge might be connected with the surrounding countryside more intimately than most large towns, it still is completely separate and distinct from the farmland that surrounds it.