Comment by mohanmca

There is no golden rule, but assume tier-2 cities mayn't have airport, no famous schools, less than 2 or 3 million people living in there.

Most of the tier-1 cities has direct international or national airways connectivity.

Tier-3 cities may not even have a single factory, it is hub for 100s villages, has decent bus-connectivity to nearest tier-2 city.