A Diamond Crossing in railway terminology is the point where two railway lines cross (not necessarily at right angles, forming the shape of diamonds at the crossing point. They are extremely rare and the most famous one, the Diamond Crossing at Nagpur is a Double Diamond Railway crossing formed by two double lines crossing each other. A lot has been said about this particular point, as the point where lines from the North, South, East and West meet and also, even as the center point of India! It is easy for such things to propagate, especially since the advent of the Internet. The real fact is that it is neither.
First, only three major rail lines meet at Nagpur junction railway station. One comes from the east, from Gondia, the Howrah – Rourkela – Raipur line. The other comes from the north, from New Delhi. The last one goes towards the South, carrying trains to both the west and the south. This line splits into two separate lines to the west (Mumbai) and the South (Kazipet) only at Wardha, some 80 km away. And only one of these lines form part of the diamond crossing, the Gondia line. The other ser of tracks forming the diamond crossing is only a service branch line from the Nagpur Freight yard which lies parallel to the passenger platforms and not even a main line. The Diamond Crossing is formed when this service line crosses over the Gondia line to join the main line towards Delhi. Sadly, it is kind of an anti-climax. You can see it in the map below.
In fact, it is not even the only Diamond Crossing in India. There is one more right smack in the middle of Delhi! There was another one at Dhanbad junction which was dismantled. There also used to be a perfect 90-degree Diamond Crossing in the new-defunct old Ernakulam Terminus as well.
The British considered Nagpur as the geographic center point of undivided India and erected the zero-mile marker there, but once India was partitioned this shifted and now as per official records the center point of India lies in a forest somewhere near Jabalpur. This village “Karondi” lies is nearest to it.
Now, railway-wise, the “real” point where the North, East, South and West of India meet is at Itarsi Junction railway station, MP. Lines from the North (towards Agra – Delhi), South (towards Nagpur), East (Jabalpur – Allahabad and then Howrah) and West (Khandwa – Mumbai) meet at Itarsi. It also is “center-ish” to India, so guess, that will do.
Here is a helpful infographic about the Nagpur Diamond Crossing