The first chapter of the book doesn't introduce us to any of the characters. Instead, we get a brief description of Chandrapore and the Marabar Caves.
The part of Chandrapore that lies by the river is grubby and sordid (i.e., dirty). But as the town slopes upward away from the river, it becomes a different city.
Upper Chandrapore is where the civil station, or headquarters for the British colonial administration, is located. Here live the British who have come to administer this particular area of India, which is a British colony at the time.
The area around Chandrapore is flat for miles and miles until you hit the Marabar Caves, which are described as "fists and fingers" jutting out of the ground (1.1.4).