(Urban) agglomerations and metropolitan areas include a central city and neighboring towns (suburbs) forming a connected region of dense, predominately urban population. Their population is economically and culturally linked to the central city (e.g., by commuters). Some agglomerations and metropolitan areas have more than one central city (e.g., the Northern Pearl River Delta or the Ruhr region). Mostly, the components of an agglomeration are small administrative divisions like communes; the gaps between built-up areas are small (e.g., less than 2km). In case of metropolitan areas, the building blocks are larger (e.g., counties or districts). Thus, the portion of rural population is typically significantly higher than for agglomerations and large gaps between built-up areas are possible. Neighboring agglomerations may be combined to a conglomeration (e.g., Randstad consisting of Amsterdam, Rotterdam and Utrecht agglomeration).
Area (A) is the total surface of a country, of its administrative divisions or of cities. It includes (non-tidal) inland water area. Land area (A-L) excludes inland water area.
Each country has its own definition what the term city means. Mostly it refers to the smallest administrative unit of a country having a predominately urban population. If a city has no legal demarcation, its boundaries are often determined for a census. Such a place is called census city or (in the USA) »census-designated place« (CDP). Smaller cities are often called towns. Rural places are often classified as villages.
A municipio is the smallest administrative unit of many countries in Latin America. It typically covers a relatively large area with several localites and has a high portion of rural population. Therefore, the urban population of a municipio is mostly tabulated as its city population.
Census population (C) is determined by a census typically performed every 5 or 10 years. The first results of census are often provisional (Cp); they may be higher or lesser than the final results (Cf). Census results mostly show some underenumeration that may be adjusted by estimates (Ca). Estimates (E) are based on calculations using the current birth and death rates and the estimated migration or they are based on population registers. Estimates refer to a given time in the past. Projections (P) are calculations referring to the future; their accuracy is often poor.
The de facto population is the population actually present at a given time including temporary residents and excluding residents temporarily absent. The de jure population (often also called resident population) is the legally resident population including residents temporarily absent and excluding temporary residents.
Urban areas (UA) are densely populated urban regions typically linked by continuous built-up areas. They may cover parts of one or of more cities or communes; their borders do not coincide with the boundaries of adminitrative units. Therefore, urban areas have more or less inhabitants than the central city. Urban population is largely non-agriculturally oriented. Each country has its own definition of urban and rural. Consolidated urban areas (CUA) combine neighbored urban areas. Some small gaps between the areas and the inclusion of small rural areas connecting the urban areas are possible. Smaller urban areas are also called urban settlements.