Prime Minister Manmohan Singh on Saturday urged all citizens to participate in Census 2011, saying that enumeration will constitute an important input in the processes of planning and development of the country.

Dr Singh, who was enumerated for the Census in New Delhi on Saturday, requested each citizen to participate in the national endeavour and ensure that every person is included in the exercise.

He also said the census is the most massive operation for compiling statistics anywhere in the world. Some of this data form an important base for planning the level of the government's economic and social activities, the PM said.

The 2011 Census will see the engagement of 25 lakh enumerators, who will ensure that every single citizen is counted. The mammoth exercise will be undertaken in two phases.

The first phase, called the House Listing and Housing Census, will be conducted between April and July this year. The second phase, called the Population Enumeration, will be conducted simultaneously all over the country between February 9 and February 28, 2011.

Meanwhile, enumerators will also collect information like ownership of mobile phones, computers, internet, having access to treated or untreated drinking water facilities, and will also obtain fingerprints and photographs, which will help the government formulate plans and strengthen the country's security.

However, the exercise has many challenges, which include coverage of a vast geographical area, widespread illiteracy, and diverse cultures and languages.