There are 4 main regions in India for tea (according to 80° 15).
Assam. ~50m above sea level. Malty, energising, 2nd flush is prized.
Darjeeling. Himalayan foothills, high elevation. Light, floral, first flush is prized.
Dooars. West Bengal plains, robust teas for blends.
Nilgiris. smooth body, brisk, fruity aroma; good for iced teas
CTC means *crush, tear, curl*, makes little droplets of fast infusion tea (as opposed to *orthodox*)