This map from Wikimedia provides information on the average annual temperature figures across the country over a range of below 20 Deg C and above 27.5 Deg C. The map reveals that:
Most of the country lies in the range of 25-27.5 Deg C, followed by 22.5-25 Deg C.
A small patch below the Himalayan range and in the Western Ghats falls in the range 20-22.5 Deg C.
The Himalayan range covering Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh and parts of Meghalaya are the coolest areas and fall in the below 20 Deg C range
A small region surrounding Gandhinagar in Gujarat, most of Coastal Andhra, Rayalseema and Coastal Tamil Nadu, are the hottest areas with a temperature range of above 27.5 Deg C.
