Is longan suitable for my area and how is it different from litchi?

Longan is a close relative of litchi and suits similar warm, subtropical to tropical, frost free areas with a slightly cooler dry spell that helps flowering, so in India it can grow in belts like parts of West Bengal, Bihar, the North East, and some southern and Western Ghats pockets where litchi or similar fruits do well. It needs deep, well drained fertile soil, protection from frost and very strong winds, and enough moisture during fruit development. Compared with litchi, longan fruit is smaller, brown skinned and stores and transports a bit better, and the tree can be somewhat hardier in some conditions, but it is still a niche crop in India with limited acreage. If litchi grows in your district, longan is worth considering as a trial. Confirm suitability and variety choice with your KVK or a horticulture station, and ideally see an existing tree fruiting nearby before planting widely.