Sometimes called Dilli is a Union Territory of India .It was formerly a Union Territory. It is made up of three main census areas-Old Delhi, New Delhi, and Delhi Cantonment, including 214 villages in the surrounding countryside. New Delhi is the capital of the Republic of India.
The Union Territory of Delhi has an area of 1,483 square kilometres. Old Delhi covers 932 square kilometres. It has a population of nearly 10 lakh. New Delhi is the official capital of India. It covers 439 square kilometres and has a population of nearly 4 lakh.

New Delhi was built by the British 5 kilometres to the south of Old Delhi in the early 1900's. But the two cities have since merged to form a single metropolis with a population of approximately one crore. This figure is used to indicate a central city area and the developed areas surrounding it. Delhi lies on the Yamuna River, a tributary of the Ganges (or Ganga), in north central India. It is about 150 kilometres south of the Himalayas.

The City: Delhi, including both Old and New Delhi, lies within a roughly three-sided area of land known as the Delhi Triangle, bounded on two sides by hills of the Aravalli range and on the third side by the Yamuna. The contrast between Old and New Delhi is striking.

Old Delhi consists of a twisted maze of narrow winding streets cut through by a few broad roads. Living conditions in Old Delhi are overcrowded and cramped. Many industries are in these heavily populated residential parts of the city.
The busiest and most colourful street is Chandni Chowk. The name literally means "silver street." But Chandni Chowk is in fact a wide boulevard measuring 21 metres across and packed with shops and stalls and multicoloured temples. It was laid out in 1650 on the orders of the Mughal princess, Jahan Ara.

New Delhi was designed by the British architect Sir Edwin Lutyens, assisted by Sir Herbert Baker. It was laid out 5 kilometres south of Old Delhi on a well-drained site standing slightly above the level of the surrounding plain. The builders used explosives to blast away the top layer of the land to flatten it and provide earth to fill in the nearby valleys. The resulting complex is a spacious, attractive, and carefully planned city, with broad, tree lined avenues and many open areas, parks, gardens, and fountains.