What is the setting of "An Astrologer's Day"?

"An Astrologer's Day" is a short story written by R. K. Narayan from his larger collection of the same title. The story takes place in a city in India, and although the city is never explicitly named within the text, it's generally assumed that it might be Malgudi—a fiction town of Narayan's creation which he frequently references in other stories.
The first location we encounter in the story—a tree-lined area along a path running through the Town Hall Park—is described as a bustling hub for many merchants, magicians, and sellers of stolen goods. The streets are flooded with crowds of people looking to make their purchases. As the day passes, this action occurs in near darkness, as this part of the city "did not have the benefit of municipal lighting" and is instead lit by flares, gaslights, and old cycle lamps. The street, thus, appears to be a "bewildering criss-cross of light rays and moving shadows." This mysterious atmosphere is of use to the astrologer, who "knew no more of what was going to happen to others than he knew what was going to happen to himself the next minute," as it creates an air of magic that covers up for his otherwise "shrewd guesswork" in predicting the destiny of his customers.

The setting of "An Astrologer's Day" is the Town Hall Park.
In the story, the vendors locate their stalls all along the path that runs through the Town Hall Park.
The text tells us that the immense crowd moves up and down this designated path from morning until night. All along the way, a variety of vendors set up shop and ply their wares to their customers. As for the astrologer himself, he takes up his usual station under a tamarind tree located next to the path.
We learn that the astrologer is usually under the tamarind tree by noon. There, he spreads out his cowrie shells, mystic charts, notebook, and bundle of palmyra writing. Since the astrologer doesn't have his own light, he has to rely on the groundnut vendor's light streaming across his stall.
So, when the groundnut vendor blows out his gaslight for the evening, his actions usually indicate that it's time for the astrologer to go home as well.

R. K. Narayan creates a strong impression of the throngs of poor people of India by giving descriptions of what there is in the park for them to see and hear. The sights and sounds include the following:
medicine sellers, sellers of stolen hardware and junk, magicians, and, above all, an auctioneer of cheap cloth, who created enough din all day to attract the whole town.
This is their entertainment. There is also a vociferous vendor of groundnuts. These nuts must be the same as, or similar to, our peanuts, which also grow underground. The picture we get it one of extreme poverty and empty lives. The people are here because they have very little money. Yet the quack medicine sellers and the various vendors are desperately trying to get whatever they can out of them. The groundnuts are probably the cheapest kind of nuts and might attract buyers who could not pay anything more for any kind of food. The astrologer himself is desperate for customers, even though "a surging crowd was always moving up and down this narrow road morning till night." He is usually surrounded by curious spectators, but none of them ventures to ask a question or part with the smallest coin.
The lighting also shows the poverty of the setting. The astrologer cannot even afford to have his own light at night.
The astrologer transacted his business by the light of a flare which crackled and smoked up above the groundnut heap nearby.
Evidently the groundnut vendor does not have a stall but dumps his merchandise directly onto the ground and lights it at night with a flare. Hardly any of the businesses had really decent lighting. Some had no lights at all but, like the astrologer, depended on other people's lights. One might think that those who were providing the lighting would resent the parasitism of their neighbors. But this would only happen if a neighbor happened to be a competitor. The astrologer did not compete with the groundnuts vendor. Instead, by attracting people and causing them to linger, the astrologer might have helped the groundnuts dealer a little—and vice versa.
When Guru Nayak bursts upon the scene, he is quite different from the other listless, impoverished people. The newcomer has money. And he is not just another idler. He seems to be in a great hurry. He has places to go. Guru Nayak seems relatively affluent, and he has a specific purpose for being there. He is looking for the astrologer—but does not know he has found him.