A rough division, but a useful one: each of these produced a distinct building tradition because it had different material and different weather to work against.
The Himalaya and the north
Mountain and foothill country running the length of the northern border, holding the headwaters of the river systems the plains depend on.
What it left: Timber-and-stone temple building, Buddhist monastic architecture in Ladakh and Sikkim, and the hill railways cut into the slopes under British administration.
The Gangetic plain
Alluvial flatland along the Ganges and Yamuna, the most densely populated part of the country and the seat of most of its imperial capitals.
What it left: Mauryan pillars, Buddhist stupas at Sanchi and Sarnath, the Delhi Sultanate and Mughal capitals, and the brick monasteries of Nalanda.
The desert and the west
Arid Rajasthan and Gujarat, where water storage determined where people could live and how much they could build.
What it left: Hill forts on defensible scarps, stepwells cut seven storeys into the ground, and the Harappan city of Dholavira with its sixteen reservoirs.
The Deccan plateau
Volcanic basalt uplands in the centre of the peninsula — rock hard enough to cut into and stable enough to hold a carved ceiling.
What it left: The rock-cut halls of Ajanta, Ellora and Elephanta, the Chalukyan temples at Pattadakal, and Vijayanagara's capital at Hampi.
The south
Granite country below the Deccan, with a temple tradition that continued unbroken where the north was repeatedly interrupted.
What it left: Pallava shore temples at Mahabalipuram, the Chola temples at Thanjavur, Hoysala soapstone carving, and living temple cities such as Madurai.
The east and north-east
Delta, hill and forest country from Odisha through Bengal to the Brahmaputra valley, with the highest rainfall in the country.
What it left: The Sun Temple at Konark, the mangrove Sundarbans, Ahom burial mounds at Charaideo, and the Vaishnava monasteries that keep Sattriya alive.