• As defined by the UN,census is “the total process of collecting, compiling and publishing demographic, economic and social data pertaining, at a specified time or times to all persons in a country or delimited territory.”
• Census provides an instantaneous photographic picture as it was of a community, which is valid at a particular moment of time. This is called the “static aspect” of the census. Secondly, it provides the trends in population characteristics, the “dynamic aspect” of the population.

Challenges to Census –

• Sponsorship: To conduct a census, vast organisation and considerable resources are needed. The census organisation has to mobilise extensive administrative machinery with adequate legislative authority. This can be done only by National Government with the cooperation of States and Local Governments.
• Defined Territory: The population figures have no meaning unless they refer to a well defined territory. The territory covered, alongwith any changes in its area in successive censuses should be clearly and explicitly stated.
• Universality: Each person present and/or residing within its scope, without omission or duplication should be included in the census to ensure completeness and accuracy of census data.
• Simultaneity: The total population enumerated should refer to one well defined point of time and the data collected should also refer to a well defined point or period of time. This is essential to an accurate count of the total population and relationship of facts about the population to a specified period of time. As a general rule, a day is fixed for the census and also a particular moment which is called the “census moment”. In India, the “Census moment” now is the sunrise of 1st March, of the census year. The fixing of the “census moment” helps the enumerators to decide which persons are to be included in the census. The persons born after the census moment or the persons dying before the census moment are to be excluded from the census. Some of the characteristics of the population like age, marital status, occupation, literacy and birthplace etc., are referred to a period of time usually from 10th February to 28th February of the census year to ensure simultaneity.
• Defined Periodicity: Censuses should be taken at regular intervals so that comparable information is made available in a fixed sequence. A series of censuses makes it possible to appraise the past, accurately describe the present and estimate the future.
• Individual Units: Census data must be collected separately for each individual so that detailed classifications may be provided in all the required combinations. A procedure of “group enumeration” is not a census in the strict sense of the term because the recording of aggregated or summarized information on the characteristics of a group of person usually precludes the cross-tabulation of data on several characteristics. Even though a well-designed “group enumeration” can produce cross-classifications of certain individual characteristics, such as sex and age, the possibilities in this respect are so limited that the procedure is not recommended for general use, particularly since it tends to result in under-enumeration of the population.
  Individual enumeration does not preclude the use of sampling techniques for obtaining data on specified characteristics, provided that the sample design is consistent with the size of the areas for which the data are to be tabulated and the degree of detail in the cross-tabulations to be made.
• Compilation and Publications: No census is complete unless the data collected are compiled and published by geographic areas and by basic demographic variables. The unpublished data is of no use to the potential users of the census data. That is why the census should be limited to very important items which can be tabulated and published in time.
• International Simultaneity: The census of any country is of greater value nationally, regionally and internationally if it can be compared with the censuses of other countries which are taken at approximately the same time. Censuses in most countries of the world are conducted in years ending in 0 or 1. In India, the decennial censuses are conducted in years ending in 1. International comparability is thus maintained. The Indian census accompanies all the above features.

Utility of Census:

• As part of an integrated programme of data collection, the population census is the primary source of basic national population data required for administrative purposes and for many aspects of economic and social research and planning. The value of the census results is increased if they can be employed together with the results of other investigations, as in the use of the census data as a base of benchmark for current statistics. The usefulness of the census is also enhanced if it can furnish the information needed for conducting other statistical investigations. It can, for example, provide a statistical frame for other censuses and sample surveys. The purpose of a continuing programme of data collection can best be served, therefore, if the relationship between the population census and other statisitcal investigations is considered when census planning is under way and if provision is made for facilitating the use of the census and its results in connexion with intercensal sample surveys, with continuous population registers, with other types of censuses and with civil registration and vital statistics, and with labour force, educational and similar statistics. The use of consistent concepts and definitions throughout an integrated programme of data collection is essential if the advantages of these relationships are to be fully realized.
• One of India’s great national leaders, the late Shri Govind Ballabh Pant said of the census as follows: “In fact in these days you cannot take up any serious administrative, economic or social work without referring to the Census Report which is an essential part of every enquiry, of every study. Even for solution of minor problems you have often to consult the Census Reports.”
• Utility in Administration and Policy: The population census provides the basic data for administrative purposes. One of the most basic of the administrative uses of census data is in the demarcation of constituenceis and the allocation of representation on governing bodies. Detailed information on the geographic distribution of the population is indispensable for this purpose. The legal and administrative status of a territorial division also depends upon the size of its population. The social and cultural data collected in the census is employed to determine the total number of seats to be reserved for members of scheduled castes and scheduled tribes in the House of People and the Legislative Assemblies of the States. The Census also gives information on the demographic and economic characteristics of the population at the district level. This information is of immense help for the administration at the district level. Information on the geographic distribution of the population, its size and its other characteristics is essential to the study and evaluation of economic and social problems, which must precede the determination of policy affecting economic and social development. Consideration of questions of employment and manpower programmes, migration, housing, education, public health and welfare, social services, economic and social planning, and numerous other aspects of the life of the country, are facilitated if accurate information about the characteristics of the population is available for civil and other administrative divisions.
• Utility of Census data for Research Purposes: The population census provides indispensable data for scientific analysis and appraisal of the composition, distribution and past and prospective growth of the population. The changing patterns of urban-rural concentration, the development of urbanised areas, the geographic distribution of population according to occupation and education, the sex and age structure of population, social and economic characteristics of population are the questions of scientific interest which are of importance both to research and practical problems of industrial and commercial growth and management.
• Utility of Census data in Business and Industry: The census data has many important uses for individuals and institutions in business and industry. It is very difficult to make a full assessment of the multiplicity of ways in which trade and business make use of the census data. A few uses of the census data can be mentioned. Reliable estimates of consumer demand for variety of goods and services depend on accurate information on the size of the population and its distribution at least by age and sex, since these characteristics heavily influence the demand for housing, furnishing, clothing, recreational facilities, medical supplies and so forth. Since the local availability of labour for production and distribution of commodities is important in determining the location and organisation of enterprises, this calls for the need of the census data.
• Census as frame for Sample Surveys: The rapidity of current changes in the size and other characteristics of populations and the demand for additional detailed data on social and economic characteristics which are not appropriate for collection in a full-scale census, have brought about the need for continuing programmes of intercensal sample surveys to collect current and detailed information onmany topics which are usually investigated at ten-year intervals in the population censuses. The census can provide the frame for scientific sample design in connexion with sample surveys, at the same time it provides becnhmark data for evaluating the reasonableness of the over-all survey results as well as a base against which changes in the characteristics investigated in both inquiries can be measured. To permit comparison of census and survey results, the definitions and classifications employed should be as nearly alike as possible consistent with the aims of each investigation. The selection of Sample units for the purpose of investigation in a sample survey has to be made from the complete list of these units. The sampling frame may be list of small areas, structures, persons, households or groups of households. The National Sample Survey is frequently using the list of census villages as frame for several social and economic investigation in rural areas of India. The Sample Registration Scheme of Registrar General’s office in India also utilises the list of census villages and blocks as frame for the registration of births and deaths. Thus the census provides the frame for subsequent sample enquiries during the intercensal period.
• Utility of Census data in Planning: The census data is indispensable for social and economic planning of the Country. The Planning Commission utilises the Census data on the distribution of population by age, sex classified by rural and urban regions, cities, town areas and social groups to analyse the growth of consumer demand and savings in the process of development. The census data also prove useful in national income estimates and estimates on differential personal incomes in rural and urban areas and the composition of rural and urban consumption of groups of goods and services and income elasticity co-efficients. An analysis of areas of different population size with different characteristics certainly serves as a basis for Government plans and investigations in basic social capital. The data on economic activity and educational levels of the individual as collected in the census is very important for manpower planning. The housing needs can also be accurately estimated by using the census data on population. Besides all these, the census data can prove very useful in the formulation of policies on education, health, agriculture, food and development of road, rail transport etc. In a nut-shell, it can be said that the census data is extremelu useful for all types of planning.
• Utility of Population Census to Electoral Rolls: Some countries have taken advantage of the enumeration for a population census to collect, at the same time, information needed for the establishment of electoral rolls. This procedure is not generally advisable because of the deleterious effect the secondary purpose might have on the quality of the census results. It increases the burden on the enumerator and it may tempt some respondents deliberately to falsify their replies to some census questions (e.g., on age or citizenship) in order to appear eligible for placement on the electoral roll.
• Utility of Population Census to other types of Censuses: Certain information collected as part of a population census, or incidential to it, can be most useful in conducting and/or utilizing the results of housing, agricultural or establishment censuses taken at about the same time or near about as the population census.
• Utility of population census to civil registration and vital statistics: Census data serve as denominators for the computation of vital rates, especially rates specific for characteristics normally investigated only at the time of the census. Conversely, census results, time-adjusted by vital and migration statistics, can provide estimates of the future size, distribution and other characteristics of the population of the total country and subnational areas. Further, census data on fertility can provide a bench-mark check on the reliability of current birth statistics. It is consequently desirable that procedures for the collection of census data, vital statistics and migration statistics be closely co-ordinated with regard to coverage, concepts, definitions, classifications and tabulations.

Source: http://censusindia.gov.in/Data_Products/Library/Indian_perceptive_link/Census_Objectives_link/censusobjectives.htm