New Delhi: see under 'Delhi' and 'National Capital Region'
New Delhi has been the capital of India since 12 December 1911. The British Government of India built it immediately south of Shahjehanabad, the Mughal capital of India. It is to the north of Delhi: Ancient section (around Mehrauli Road).
'New Delhi' is the name of a parliamentary constituency that roughly corresponds to the areas built by the British between 1911 and 1947.
Union Territories are administrated by the President of India acting to such extent, as he thinks fit, through an Administrator appointed by him. Delhi is a Union Territory, officially known as The National Capital Territory of Delhi.
The name of the whole city, thus, is Delhi. 'New Delhi' is the name of a) a parliamentary constituency; b) the area built by the British, and c)postal zones covering almost all housing and office districts that were buil,'t after 1947, as well as the zone built by the British between 1911 and 1947.
Even those who live in New Delhi refer to their city as 'Delhi,' not as an abbreviation or out of force of habit but because their city is called Delhi. 'New Delhi' is only an administrative unit.
Therefore, for articles about New Delhi please see under 'Delhi' and 'National Capital Region.'