The actual division between the two new dominions was done according to what has come to be known as the 3 June or Mountbatten Plan.
The border between India and Pakistan was determined by a British Govt-commissioned report usually referred to as the Radcliffe Line after the London Lawyer, Sir Cyril Radcliffe, who wrote it. Pakistan came into being with two non-contiguous enclaves , East Pakiistan (today separated as Bangladesh) and West Pakistan, separated geographically by India which was formed out of the majority Hindu regions of the colony and Pakistan from the majority Muslim areas.
On 18 July, 1947,the British Parliament passed the Indian Independence Act that finalized the partition arrangement. The Govt of India Act 1935 was adopted to provide a legal framework for the two new dominios.Following partition, Pakistan was added as a new member of the United nations. The union formed from the combination of the Hindu states assumed the name India which automatically granted it the seat of British India, (a UN member since 1945) as a successor state.
The 625 Princely States were given a choice of which country to join.
Geography of the Partition ;
The Punjab -- the region of the five rivers east of Indus: Jhelum, Chenab,Ravi, Beas and Sutlej -- consists of interfluvial doabs, or tracts of land lying between two confluent rivers. These are the Sind-Sagar doab (between Indus and Jhelum), the Jech doab (Jhelum-Chenab), Rechna doab (Chenab-Ravi), Bari doab (Ravi-Beas), Bist doab (Beas-Sutlej). The main disputed areas appeared to be in the Bari doab and Bist doab,although some area in Rechna doab were claimed by the Congress and Sikhs. In the Bari doab, the districts of Gurdaspur, Amritsar,Lahore, and Montgomery were all disputed.
All these districts (other than Amritsar, which was 46.5% Muslim) had Muslim majorities, albeit,in Gurdaspur, the Muslim majority, at 51.1% was slender.
there were some discrepencies that were decided by commission.
