Raipur was made the capital because it sits almost at the centre of Chhattisgarh
Background
The Raipur district administration records that the district, being geographically located almost at the centre of the Chhattisgarh State, was made its capital. The Mahanadi and the Kharun are named as the major rivers of Raipur district. The district was divided into three parts in the year 1998, and its boundaries were reduced again in 2011 as new districts were carved out. The district record names the plains of Dharsiwa, Arang, Abhanpur and Tilda as part of its territory. Raipur today is the seat of the State government and of the new capital complex at Naya Raipur, also called Atal Nagar.
In plain words
Naya Raipur Naya Raipur (Atal Nagar) — The planned new capital city built next to Raipur for Chhattisgarh's government offices.