United Nations in the context of "Alpha Ridge"

The United Nations uses three definitions for what constitutes a city, as not all cities in all jurisdictions are classified using the same criteria. Cities may be defined as the cities proper, their metropolitan regions, or the extent of their urban area. A complicating factor is that many large cities in the world have not only homeless or the unhoused, but also vast slum communities. This leads to official census data being less accurate in representing the actual number of residents in a given area.

A country is an area of land, which has its own government and laws, or used to have them, such as a state, a nation, a nation state, or other political entity. When referring to a specific polity, the term "country" may refer to a sovereign state, a state with limited recognition, a constituent country, or a dependent territory. Most sovereign states, but not all countries, are members of the United Nations.

There is no universal agreement on the number of "countries" in the world with a range between 193 to 237. This ambiguity is a result of several states having disputed sovereignty status or limited recognition, and a number of non-sovereign entities are commonly considered countries. The definition and usage of the word "country" has fluctuated and changed over time. The Economist wrote in 2010 that "any attempt to find a clear definition of a country soon runs into a thicket of exceptions and anomalies."

In world demographics, the world population is the total number of humans currently alive. It was estimated by the United Nations to have exceeded eight billion in mid-November 2022. It took around 300,000 years of human prehistory and history for the human population to reach a billion and only 218 more years from there to reach 8 billion.

The human population has experienced continuous growth following the Great Famine of 1315–1317 and the end of the Black Death in 1350, when it was nearly 370,000,000. The highest global population growth rates, with increases of over 1.8% per year, occurred between 1955 and 1975, peaking at 2.1% between 1965 and 1970. The growth rate declined to 1.1% between 2015 and 2020 and is projected to decline further in the 21st century. The global population is still increasing, but there is significant uncertainty about its long-term trajectory due to changing fertility and mortality rates. The UN Department of Economics and Social Affairs projects between 9 and 10 billion people by 2050 and gives an 80% confidence interval of 10–12 billion by the end of the 21st century, with a growth rate by then of zero. Other demographers predict that the human population will begin to decline in the second half of the 21st century.

Sovereignty can generally be defined as supreme, independent control and lawmaking authority over a territory. It finds expression in the power to rule and make law. Sovereignty entails hierarchy within a state as well as external autonomy for states. In any state, sovereignty is assigned to the person, body or institution that has the ultimate authority over other people and to change existing laws. In political theory, sovereignty is a substantive term designating supreme legitimate authority over some polity. Under international law, sovereign states are all considered equal, and no state can interfere with the internal affairs of another sovereign state. While Article 2(7) of the UN Charter explicitly recognizes the sovereignty of states, and in general there is a principle of non-interference in the domestic affairs of sovereign states, the UN Security Council’s Chapter VII powers clearly contemplate the use of force against a state when necessary to restore peace. Further, the recent Responsibility to Protect (R2P) authorizes the United Nations to take action to “avert a humanitarian catastrophe” within a state when that state’s government cannot or will not act.

A state is generally considered to have sovereignty over a territory when it has consistently exercised state authority there without objection from other states. De jure sovereignty refers to the legal right to do so; de facto sovereignty refers to the factual ability to do so. This can become an issue of special concern upon the failure of the usual expectation that de jure and de facto sovereignty exist at the place and time of concern, and reside within the same organization.

A city proper is the geographical area contained within city limits. The term proper is not exclusive to cities; it can describe the geographical area within the boundaries of any given locality. The United Nations defines the term as "... the single political jurisdiction which contains the historical city centre."

City proper is one of the three basic concepts used to define urban areas and populations. The other two are urban agglomeration, and the metropolitan area. In some countries, city limits that act as the demarcation for the city proper are drawn very wide, in some very narrow. This can be cause for recurring controversy.

The Greater Tokyo Area is the most populous metropolitan area in the world, consisting of the Kantō region of Japan (including Tokyo Metropolis and the prefectures of Chiba, Gunma, Ibaraki, Kanagawa, Saitama, and Tochigi) as well as the prefecture of Yamanashi of the neighboring Chūbu region. In Japanese, it is referred to by various terms, one of the most common being Capital Region (首都圏, Shuto-ken).

As of 2016, the United Nations estimates the total population at 38,140,000. It covers an area of approximately 13,500 km (5,200 mi), giving it a population density of 2,642 people/km. It is the second-largest single metropolitan area in the world in terms of built-up or urban function landmass at 8,547 km (3,300 mi), behind only the New York City metropolitan area at 11,642 km (4,495 mi). With over US$2 trillion in GDP, Tokyo remains the second-largest metropolitan economy in the world, also behind New York.

This is a list of countries and dependencies by population. It includes sovereign states, inhabited dependent territories and, in some cases, constituent countries of sovereign states, with inclusion within the list being primarily based on the ISO standard ISO 3166-1. For instance, the United Kingdom is considered a single entity, while the constituent countries of the Kingdom of the Netherlands are considered separately. In addition, this list includes certain states with limited recognition not found in ISO 3166-1. Also given in a percentage is each country's population compared with the world population, which the United Nations estimated at 8.232 billion as of 2025.

A slum is a derogatory term for a highly populated urban residential area consisting of densely packed housing units of weak build quality and often associated with poverty. The infrastructure in slums is often deteriorated or incomplete, and they are primarily inhabited by impoverished people.

Although slums are usually located in urban areas, they can be located in suburban areas where housing quality is low and living conditions are poor. Slum residences vary from shanty houses to professionally built dwellings which, because of poor-quality construction or lack of basic maintenance, have deteriorated. While slums differ in size and other characteristics, most lack reliable sanitation services, supply of clean water, reliable electricity, law enforcement, and other basic services. The United Nations defines slums as ".... informal settlements lacking one or more of the following conditions: access to improved water, access to improved sanitation, sufficient living area, housing durability, and security of tenure."

The United Nations comprise 193 sovereign states and the world's largest intergovernmental organization. All members have equal representation in the United Nations General Assembly.

The Charter of the United Nations defines the rules for admission of member states. Membership is open to all states which accept certain terms of the charter and are able to carry them out. New members must be recommended by the United Nations Security Council. In addition to the member states, the UN also invites non-member states to be observer states at the UN General Assembly. A member state that has persistently violated the principles of the United Nations Charter can be expelled from the United Nations.