That

According to Vishnu Narayan Bhatkhande (1860-1936), one of the most influential musicologists in the field of North Indian classical music in the twentieth century. He tried to classify Hindustani Raagas a full 270 years after Venkatamakhin He toured important centers of Carnatic music like Tanjavur, Madras and Mysore and studied the Melakartha scheme of Venkatamakhin. It was clear that he could not directly use the Mela system. Of the six combinations given below, Hindustani does not allow the bottom two combinations in either lower tetrachord or upper tetrachord, since, Hindustani does not use both Gandharas (komal ga and shudh Ga) without using even one variety of Re or both Rishabs (komal re and shudh Re) without using one variety of Ga etc. Using 4 combinations in each tetrachord would have given 4x4x2=32 Melas (or Thats, to use a Hindi word).

सा रे - - ग म प ध - - नी सा
सा - रे - ग म प - ध - नी सा
सा - रे गा - म प - ध नी - सा
सा रे - ग - म प ध - नी - सा
सा रे रे - - म प ध ध - - सा (not possible in Hindustani)
सा - - ग ग म प - - नी नी सा (not possible in Hindustani)

But, Bhatkhande decided to not use this scheme, after seriously considering it. One reason was that for some of the scales, there were no existing Raagas. Instead of using all the Melas for which Raagas existed, for ease of memorization, Bhatkhande came up with a ten That (meaning framework) system. These were like the Genera and each Raaga classified under it was a species belonging to the Genera (plural of Genus, as used in biology). Each of the thats were named after the most famous Raaga using that scale. Incidentally, six of the thats are ancient scales got through Moorchana.

Thaat	Scale	Characteristics
Bilaval	सा रे ग म प ध नी सां	All shudh or natural notes
Khamaj	सा रे ग म प ध नी॒ सां	नी note as komal
Kafi	सा रे ग॒ म प ध नी॒ सां	ग and नी notes as komal
Asavari	सा रे ग॒ म प ध॒ नी॒ सां	ग, ध and नी notes as komal
Bhairavi	सा रे॒ ग॒ म प ध॒ नी॒ सां	रे, ग, ध and नी notes as komal
Bhairav	सा रे॒ ग म प ध॒ नी सां	रे and ध notes as komal
Poorvi	सा रे॒ ग मे प ध॒ नी सां	रे and ध notes as komal and the म note as teevra
Todi	सा रे॒ ग॒ मे प ध॒ नी सां	रे, ग and ध notes as komal and the म note as teevra
Marwa	सा रे॒ ग मे प ध नी सां	रे note as komal and the म note as teevra
Kalyan	सा रे ग मे प ध नी सां	म note as teevra only

There were several well known Raagas which do not fit any of these scales, but were subjectively grouped under one of the thats by Pt. Bhatkhande. For this reason, his classification has not been universally accepted, though its is the system that has been accepted most.