In "The Postmaster" by Rabindranath Tagore, what do we come to know about Calcutta?

The postmaster sees Calcutta as more desirable than Ulapur.

The opening description of Calcutta reveals how the postmaster feels out of place in Ulapur.  The postmaster "felt like a fish out of water in this remote village." Calcutta is seen as cosmopolitan, full of insightful and well-read people that more closely mirror the postmaster's predispositions.  The postmaster cannot appreciate Ulapur's people, whom he saw as "hardly desirable companions for decent folk."  

The postmaster also sees Calcutta as more hygienic than the village.  When he gets sick from the rains, the postmaster "at once wrote off to Calcutta an application for a transfer, on the ground of unhealthiness of the place."  The postmaster sees Ulapur as the reason for his illness.  This emphasis on the hygiene of Calcutta can be seen on the last day of the postmaster's stay. Unlike most people of Ulapur, who bathe in the local river, the postmaster "had stuck to his Calcutta habit of bathing in water drawn and kept in pitchers."  

When the postmaster tells Ratan that he is leaving, he says he is "going home."  Calcutta is where the postmaster's heart lies.  The postmaster's references lead us to see Calcutta as a place with more physical and cultural conveniences than than Ulapur's rural setting.