There is actually a maritime law behind showing Sri Lanka in the Indian map. If Sri Lanka is not shown in the Indian map then it will be considered a legal offence. This is the reason why Sri Lanka is definitely shown in every Indian map.
What does the law related to this say
This law was made by the United Nations, which is called Law of the Sea. According to this, if a country's border is bordered by the sea, then the sea area up to about 200 nautical miles i.e. about 370 kilometers will be considered the sea area of that country. Sri Lanka also comes within this maritime border of India. Actually, the distance from Dhanushkodi of India to Sri Lanka is only 18 kilometers, hence due to the Law of the Sea, it has been made mandatory for India to show Sri Lanka in its map.
Why was this law made
In the year 1956, when the United Nations Convention on the Law of the Sea was organized by the United Nations, many countries participated in this conference. During this period, there was an in-depth discussion on maritime boundaries and related treaties and agreements. However, this law was recognized in its third conference which took place between 1973 and 1982. During this period, many maritime international laws were recognized, one of which was the Law of the Sea. Under this, it was made mandatory to show the limit of 200 nautical miles from the baseline of that country on the map of any country.