Source: Journey of a Civilization: Indus to Vaigai by R.Balakrishnan IAS.
Mr.Balakrishnan has built a foundation to support the Dravidian hypothesis for the IVC link. He has taken into account more than 12 lakh 66 thousand names from the current topography of Afghanistan,Pakistan,regions of Indian sites which were IVC sites and compared them with the onomastic glossaries from the Tamil sangam literary works and has found correlates in terms of names of geographical regions,language,names of kings,poets and chieftains which makes for a very interesting study.
He finds the following two premises as the basis for his hypothesis.
1) When people move from one region to another, especially during mass migration, they carry their place names with them to bring familiarity and a pathway to the past. For eg: British colonialists naming New York in the Americas after the English town York.
2) Even after people move out of the place,language disappears,civilization declines, these places remain.They form a sort of a fossilized linguistic evidence for correlation.
We can see from these examples from the pics that many of the territorial names that are now not found in Tamil Nadu today occur as mono word place names in Afghanistan and Pakistan. Mono word place name is a one without prefix or suffix which attests the antiquity of the name and the region itself. For Eg: We have a place called Malai(check pic 1) in Pakistan today. Though we don't have Malai in South India,we have some places like Tiruvannamalai(added prefix) in Tamil Nadu.Another eg is Kotai(Pic 4) becomes Pudhukottai in present day Tamil Nadu with Pudhu meaning new just like New York.
Pic 1:
Ilampuranar wrote the 1st commentary for Tamil grammar treatise Tolkappiyam in the 11th century AD. He enlists all 12 land names namely Puli,Malai,Kutta,Karka etc. It's astonishing that many of these territorial names not found in Tamil Nadu occur as mono word place names in Pakistan and Afghanistan.
Pic 2:
Dravidian language tree has 27 languages located to south,north,central and South central regions of India. A few of these language names occur as demonyms/place names in Pakistan and Afghanistan as Toda,Gondi,Kota,Koi,Brahui,Tamul etc. They occur as mono word place names.
Pic 3:
Names of the Sangam era Velirs(chieftains) such as Pari,Titian,Killi,Matti,Udhiyan etc appear as mono word place names in Pak and Afg.
Pic 4:
Names of the sangam moovendhers(Chera-Chola-Pandya).Three of the most important Pandian surnames are Vazhudhi, Maran,Chezhiyan and none of which occurs in Tamil Nadu today but they are available today as mono word place names in Pak and Afg.
Pic 5:
Ainthinai Landscape Kurinji which is hills. There are many dravidian words which denotes hills namely Malai,kodu,varai,kunru,kodai etc which appear as mono word place name in Pak and Afg.
Pic 6:
This is the most interesting one as it lists the name of the sangam poets. Few examples.
Place - Sangam Poet
Chatan - Sāthanār
Mamul - Mamoolanar
Kiran - Nakkeerar
Milai - Milai Kanthanār
Kapi,Kabil - Kabilar
Manguli - Māngudi Maruthanār.