Since there is no official divisions of regions and different media houses have their own, I have made my own divisions and subdivisions. Here's what it looks like.
Chennai : Essentially comprising just Chennai district. Most other divisions keep it as 16 seats, but my guess is that the politics spills over into the entire district and not just the metropolitan area.
The other regions are described in more detail in the following posts.
[1/n]
North : The basins of the Palar and Thenpennai [and a bit of the Kaveri]. Politically dominated by the politics of the PMK and DMDK. The dry erstwhile industrial heartland.
PeriChennai - The overflow of Chennai politics. Much more urban. In some sense the ends of Chennai suburban rail. Chengalpattu, Kanchipuram and Tiruvallur.
North Arcot - Vellore, Ranipet, Tirupattur and Tiruvannamalai.
South Arcot - Villupuram, Cuddalore and Kallakurichi
Baramahal - Dharmapuri and Krishnagiri
[2/n]
Kongu : the upper Kaveri basin to the western border. The wet current industrial heartland.
Baramahal - Salem
Ponni - the districts directly on the Kaveri. Erode, Namakkal and Karur
Kovai - Coimbatore
Mountain Kongudom - The Nilgiris
Union - the highly industrialized bit of Kongu. Tiruppur and Dindigul
Some of the divisions may seem a little random. Just dividing it this way to see if they form separate political blocks.
[3/n]
Delta : the lower Kaveri basin and the Kaveri delta. In most divisions this region is bigger. I have removed Cuddalore and Pudukottai from this region as I felt their politics was more similar to their other neighboring regions.
Western Chola - Tiruchirapalli, Ariyalur and Perambalur
Central Chola - Thanjavur and Tiruvarur
Coastal Chola - Mayiladuthurai and Nagapattinam
Though delta politics is quite homogeneous, I made the divisions because I suspect there may be a change in 2026.
[4/n]
South : The varied lands south of Madurai. From saltpans, coastlines, ports, shadows of the Western ghats and the tip of Tamil Nadu.
Ramnad - the remnants of historical Ramnad kingdom. Pudukottai, Sivagangai and Ramanathapuram.
Central Pandya - the bulk of the South. Madurai, Thenkasi, Theni, Virudhunagar and Thoothukodi.
Cape - also known as Karunanidhi's conundrum. Characterized by the remnants of imperial politics. Also in some cases an overflow of Kerala politics.
[5/n]
And finally here is all the subregions and their respective contributions to Tamil Nadu electoral politics.
The divisions have been made with a number of criteria - from Sangam, colonial, imperial and relatively modern TN politics. The aim is to see if they do form distinct political blocks.
I wanted to establish this classification before looking at the rest of the data.
[6/n]
Raboniel Shadowsong