If you want to see a regularly updated map of Indian Railways you can find it here [1]. This map has a lot of contributions from users and has details about new lines, lines under upgradation, electrification status.

This website can also show a route particular train takes in India fairly accurately. For example here is route map of Vivek express, covering longest distance, 4,218.6 kilometres (2,621.3 mi) in single journey [2].

[1] https://indiarailinfo.com/atlas

[2] https://indiarailinfo.com/train/map/route-dibrugarh-kanniyak... [2]