Calcutta, actually called Kolkata, is significant to Jane Eyre because Calcutta was a colonial city that was colonized by the British. Kolkata was colonized by the British in 1690 by an agent of the English East India Company named Job Charnock. The colonization began as he built a trading outpost on the bank of the Hooghly River, and after tons of economic growth, Kolkata became the capital of British India in 1772. This information comes from a website called Britannica. This location illustrates colonization and empire because Kolkata was still a British colony during the production of Jane Eyre. This place is mentioned by Diana in a conversation with Jane, and she says, "You are much too pretty, as well as too good, to be grilled alive in Calcutta" (Bronte, 370). This is a conversation about how dangerous it is to travel to India as a missionary. Diana saying Jane is 'too pretty' and 'too good' implies that she believes that India is a more primitive society, as it is 'worse' than their own. Becoming a Christian missionary is also another form of colonization, as it is bringing a new belief system into a place that did not entirely want it. Mapping this location on Cove reveals how this place connects the novel to Britain's wider colonial and economic history.
Research: https://www.britannica.com/place/Kolkata/History