Difference between North and South India are so stark and vivid that it would take a book to compile all of them. So it is better to start from the outset.
Geographical differences
North India lies in the Indo-Gangetic plain surrounded by Himalayas, while South India is demarcated by Deccan plateaus and small hills. North India is landlocked while South India is surrounded by Arabian Sea and Indian Ocean.
Climatic differences
The climate in North India is generally cool and dry in winters and very hot in summers while the temperatures are high throughout the year in South India with high humidity due to proximity to the sea. There are regional differences with both North and South India.
Linguistic differences
Languages in North India have originated from Devnagri lipi, while in South India language originated from Dravidian lipi. There are again regional differences with lots of language in both parts of India.
Cultural differences
Historically ruled by Aryans, Mouryans, and Mughals, culture in North India has had several influences which are evident in art and dance forms such as kathak, while South India was ruled by Cholas, Pandiyas etc and the culture is known as Dravidian culture untouched by influences from North.
Dress differences
Salwar kurta is used by women in North India while men wear shirt and pants, while in South India, women wear saris and men wear dhotis. However, these dressing styles are merging with western influences and boys and girls in both parts are today wearing jeans.
Cuisines
Cusines of North and South India are starkly different. While wheat is the staple food in North, it is rice in South India. North Indian food is spicier and heavier, while food in South India is nutritious and light. North Indian recipes that are non vegetarian are also known as Mughlai dishes. North Indians make more use of milk based products, while South Indians consume yoghurt more.
Religion
Though there are Hindus both in North and South India, they practice different customs and traditions and have different idols or gods. Even temples in both parts are different with differences in architecture. South Indian temples are more lavish and grand than those in North India.
Literacy
South India is far ahead when it comes to literacy and they are more literate than North Indians.
Development
South India is more developed and planned than North India. People in south are generally soft while people are aggressive in North India.