Apart from being a full enumeration of the population of Hong Kong, Population Census and By-Census are also the primary sources of data for small geographical areas and population sub-groups.

The information collected in population censuses/by-censuses is vital to government planning and policy formulation, particularly in such fields as education, housing, transport, medical and social services. Data on small areas form the basis of district development and service planning programmes of the government, while comprehensive information on population sub-groups, such as the elderly and single parent families, facilitates the planning of welfare policy and social service programmes. Most important of all, results of the censuses/by-censuses are the benchmark data for the compilation of population estimates in the Population Data System.

The system for compiling population estimates is complex and requires data from a wide variety of sources. The results of population censuses/by-censuses form the corner stone of the system. These benchmark data are taken together with statistical data generated from administrative systems (such as birth, death and passenger movement records) and sample surveys (in particular the continuous General Household Survey) to form a population statistical database which serves a multitude of purposes, including amongst which the compilation of population estimates.

According to the schedule, the Census and Statistics Department will release at end-August 2001 the provisional population estimates for mid-March 2001 (i.e. the Census Moment) and end-June 2001. Basic information collected in the 2001 Population Census will be used in the compilation of these estimates. However, since "Hong Kong Resident Population" refers to "Usual Residents" and "Mobile Residents", and the compilation of statistics on "Mobile Residents" requires data generated from the passenger movement record system for the six months after the reference period, the revised population estimates for mid-March will not be available until October (i.e. upon complete information on passenger movements up to mid-September is available).

Other detailed statistical data compiled on the basis of the 2001 Population Census will be released in phases as from the latter part of October 2001, starting with a set of basic tabulations. The revised population estimates for mid-March will be released in parallel with other data in October. As for the revised mid-year population estimates for 2001, they will be released in accordance with the usual release schedule, that is, in February 2002.