The biggest demographic exercise ‘Census-2011" will take off today covering over 1.2 billion residents of the country across all states and union territories. The mammoth operation will start with President Pratibha Devi Singh Patil becoming the first citizen to be enumerated at 10 am, followed by Vice-President Hamid Ansari. <br/><br/>Census 2011 will mark a milestone as the National Population Register (NPR), which will create a comprehensive database of all residents complete with the photographs and finger prints of all persons above 15 years of age as well as specific information about each of the individual. AIR correspondent says that for the first time the census will also measure the usage of mobile phones & computers, reach of internet & banking services . <br/><br/>Amenities like availability of potable water and other basic amenities the house hold possesses will be the crucial part of the house listing process of the first phase of census which will be conducted between April to September this year. The second phase of the operation will involve population enumeration which will be carried out between 9th and 28th of February next year. 25 lakh personnel will be engaged in the whole exercise.