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The terms city limits and city boundary refer to the defined boundary or border of a city. The area within the city limits is sometimes called the city proper. The terms town limits/boundary and village limits/boundary mean the same as city limits/boundary, but apply to towns and villages. Similarly, the term corporate limits is a legal name that refers to the boundaries of municipal corporations. In some countries, the limits of a municipality may be expanded through annexation.
City limits in the United States and Canada 
In the United States, such limits are usually formally described in a state, provincial, or territorial law (or an appropriate regulation) as being under the control of the municipal corporation or agency that constitutes the city government. It is customary to indicate city limits with the posting of signs on major freeways, highways, and arterial roads. Note that New England states have a unique concept of "towns", which are similar in size to the civil townships in other States, but empowered with the authority exercised by municipalities in other States.
Property within city limits is subject to city taxation and city regulation, and expects city services. Areas outside of any city's limits are considered to be unincorporated, and in most U.S. states they are by default regulated and taxed by the county. In others, areas outside of city limits fall within another type of local government, such as the civil township (a division of a county). Cities and towns may have extraterritorial jurisdiction beyond their limits, typically for zoning purposes. The distance this extends varies based on the population or area of the city, or which "class" it is considered to be under state law.
Home rule within a city's limit is usually exercised by the mayor (executive branch) and city council (legislative branch). Home rule outside the city limits is usually exercised by the county commission (which is often both legislative and executive), or the township's board of supervisors. Even without home rule, the county, as a unit of state government, also has certain powers and responsibilities even within the limits of its cities, including the sheriff that performs evictions, runs the county jail that all city and county police departments take arrested persons to, and guards the courthouse for the county's state court even though it is usually within the city limit of the county seat. Elections and health departments are also common county responsibilities which include all cities. (City residents still pay some county taxes for these reasons.)
If a city chooses to have its own emergency services, they only have jurisdiction within the city limits, except for mutual aid (typically among fire departments) in case of disaster. Telephone companies also must keep track of changing city limits to ensure that calls to 9-1-1 are routed to the appropriate public-safety answering point, if the city operates a PSAP separate from the county. Calls from mobile phones are usually routed based on the location of the base station rather than the calling party, so these (along with landline calls to non-emergency telephone numbers) must be handled manually by the telephone operator or dispatcher, determining whether the caller or incident is within a particular city limit or not so that the proper authorities may be sent.
City limits may extend into more than one county, which can complicate certain matters of policing and taxation. (For example, sales tax revenue collected in a city by one county may not be spent in another part of the city outside of that county.) Where a city merges its government with that of its county to become a consolidated city-county, the city limits are usually considered to be expanded to occupy all of the previously-unincorporated area of the county, while other existing municipalities continue to exist but are permanently locked into their city limits without the possibility of annexation (except possibly into a neighboring county). An independent city's limits separate it from being in any county at all. Similarly, cities and towns may or may not be considered part of the township[s] they are in.
City, town, and village limits are not usually coterminous with post office locations or ZIP codes/ postal codes, and the USPS and Canada Post even considers some places to be "unacceptable" for use on mail. (For example, parts of Sandy Springs within its city limit but outside of 30328 must use "Atlanta, GA" instead.) School districts and other special-purpose districts may be overlaid on cities, or cities may choose to have their own — however, these are often under other authorities.
City boundaries in the United Kingdom 
In the UK, city boundaries are more difficult to define, since British cities are defined as any town, regardless of size, that has been granted letters patent. In smaller cities, such as Wells (pop. approx. 10,000) or Gloucester (pop. approx. 100,000), the boundary will be that governed by the city council. In the case of larger cities, such as Birmingham (pop. approx. 1,000,000), a specific metropolitan borough will make the definition. Ironically, London the largest city is perhaps the most difficult to define, as different people have different definitions ranging from just The City of London, to anywhere inside the M25 motorway.
Although British city boundaries are often important for defining local services such as refuse collection, schools, libraries and planning (zoning), they play little or no role in law enforcement or hospitals. Police jurisdiction and local services are generally defined by county boundaries, and people in one county may usually decide to use hospitals, libraries, and schools in another without incurring any fees.
There is no concept of local taxation in the UK, other than minor differences between Northern Ireland, Scotland and England and Wales. Local government councils derive their income from council tax and business rates, which are based on the values of buildings.
Planning (zoning) law around British cities is generally determined by green belt laws, which prevent building on the countryside immediately surrounding large and medium-sized towns and cities.
See also