From the perspective of the relationship between resources and humans and the relationship between the environment and humans, there is a quantitative limit to the population on the earth: population = area suitable for human habitation/site required for individual production and life. The formula is expressed as: X =S/s=aS. Among them, The above formula X=aS can be called the population law.
From the perspective of production and living needs, each human being requires 1,500 square meters of space for production and living. From the population law formula X=aS and the area suitable for human habitation on the earth and the space required for each individual's production and life is 1500 square meters, the upper limit of the earth's population can be calculated.
The modern census refers to the nationwide survey and registration of the entire population, household by household, and person by person, within a time period uniformly stipulated by the state, according to unified items, unified forms, and unified filling methods. It is a large-scale social investigation with strict organizational leadership, careful planning, and scientific methods. The United States began conducting censuses in 1790, making it the first country to conduct a census.
The United Nations census contains 36 items, including population migration, family, fertility, mortality, education, economy, housing and other characteristics. Some countries have more census items. For example, the United States had 65 projects in 1980, Canada had 69 projects in 1981, India had 40 projects in 1981, and the Philippines had 41 projects in 1980.
Census information has legal effect. Its role can be summarized in the following three aspects: (1) Formulating policies, allocating electoral quotas, and formulating construction plans. For example, the U.S. Constitution stipulates that a census be conducted every 10 years in order to accurately allocate seats in the House of Representatives, determine the number of members of each state in proportion to population, and determine the federal government's funding for each state. (2) Used to study the regional distribution, fertility, death, growth, gender, age, urban and rural areas, occupation, culture and other characteristics of the population. (3) Determine the supply of housing equipment, food, clothing, entertainment facilities, medicine, etc., the layout of commercial outlets, and the distribution of goods and labor based on the information on population size, distribution, age, gender, etc. obtained through the census.
Census information is only a small member of the vast information family of Digital Earth. Digital Earth can integrate census information and other geospatial data. For example, population information can be archived and managed uniformly by department and administrative unit, and it can echo the spatial characteristics of ground objects (such as ground object images) through the Internet. Through Digital Earth, people can browse a series of electronic maps (such as terrain, water systems, land use, population distribution, etc.) and explanatory text of a country or region on the earth, and obtain detailed information about the population and its living space, including the total population. , male to female ratio, education level, ethnicity, occupation, economy, education, commerce, medical and health, public welfare, employment and social insurance, etc. Detailed information including photos can be obtained by visiting the profile page.
Census information is widely used for population analysis and projections. By interpreting high-resolution satellite images, scientists can obtain information on urban ground buildings and estimate the population of residential areas. Digital Earth, supported by satellite remote sensing, geographic information systems and Internet technology, has powerful analysis, evaluation and simulation capabilities. For example, scientists in Pendleton, California, USA, can simulate the impact of different population growth on biodiversity by collecting information on terrain, soil type, annual rainfall, vegetation, land use and land ownership. For another example, through census data, the dynamic growth, population distribution and population migration of urban population can be simulated. Immigration issues in large-scale engineering projects like the Three Gorges Project can be solved with the help of Digital Earth's network functions, interoperability and geographic information system technology.