In demographics, the centre of population (or population center) of a region is a geographical point that describes a centrepoint of the region's population. There are several different ways of defining such a "centre point", leading to different geographical locations; these are often confused.
Three commonly used (but different) center points are:
A further complication is caused by the curved shape of the Earth. Different centre points are obtained depending on whether the centre is computed in three-dimensional space, or restricted to the curved surface, or computed using a flat map projection.
The mean center, or centroid, is the point on which a rigid, weightless map would balance perfectly, if the population members are represented as points of equal mass.
Mathematically, the centroid is the point to which the population has the smallest possible sum of squared distances. It is easily found by taking the arithmetic mean of each coordinate. If defined in the three-dimensional space, the centroid of points on the Earth's surface is actually inside the Earth. This point could then be projected back to the surface. Alternatively, one could define the centroid directly on a flat map projection; this is, for example, the definition that the US Census Bureau uses.
Contrary to a common misconception, the centroid does not minimize the average distance to the population. That property belongs to the geometric median.
The median centre is the intersection of two perpendicular lines, each of which divides the population into two equal halves. Typically these two lines are chosen to be a parallel (a line of latitude) and a meridian (a line of longitude). In that case, this center is easily found by taking separately the medians of the population's latitude and longitude coordinates. Tukey called this the cross median.
The geometric median is the point to which the population has the smallest possible sum of distances (or equivalently, the smallest average distance). Because of this property, it is also known as the point of minimum aggregate travel. Unfortunately, there is no direct closed-form expression for the geometric median; it is typically computed using iterative methods.
In practical computation, decisions are also made on the granularity (coarseness) of the population data, depending on population density patterns or other factors. For instance, the centre of population of all the cities in a country may be different from the center of population of all the states (or provinces, or other subdivisions) in the same country. Different methods may yield different results.
Practical uses for finding the center of population include locating possible sites for forward capitals, such as Brasília, Astana or Austin. Practical selection of a new site for a capital is a complex problem that depends also on population density patterns and transportation networks.
It is important to use a method that does not depend on a two-dimensional projection when dealing with the entire world. As described in INED (Institut national d'études démographiques), the solution methodology deals only with the globe. As a result, the answer is independent of which map projection is used or where it is centered. As described above, the exact location of the center of population will depend on both the granularity of the population data used, and the distance metric. With geodesic distances as the metric, and a granularity of 1,000 kilometers (600 mi), meaning that two population centers within 1000 km of each other are treated as part of a larger common population center of intermediate location, the world's center of population is found to lie somewhere north of South Asia with an average distance of 5,200 kilometers (3,200 mi) to all humans. The data used in the reference support this result to a precision of only a few hundred kilometers, hence the exact location is not known. Another analysis utilising city level population data found that the world's center of population is located close to Almaty, Kazakhstan.
China's population centroid has wandered within southern Henan from 1952 to 2005. Incidentally, the two end point dates are remarkably close to each other. China also plots its economic centroid or center of economy/GDP, which has also wandered, and is generally located at the eastern Henan borders.
The center of population of Estonia was on the northwestern shore of Lake Võrtsjärv in 1913 and moved an average of 6 km northwest with every decade until the 1970s. The higher immigration rates during the late Soviet occupation to mostly Tallinn and Northeastern Estonia resulted the center of population moving faster towards north and continuing urbanization has seen it move northwest towards Tallinn since the 1990s. The center of population according to the 2011 census was in Jüri, just 6 km southeast from the border of Tallinn.
In Finland, the point of minimum aggregate travel is located in the former municipality of Hauho. It is moving slightly to the south-west-west every year because people are moving out of the peripheral areas of northern and eastern Finland.
The centre of population in Great Britain did not move much in the 20th century. In 1901, it was in Rodsley, Derbyshire and in 1911 in Longford. In 1971 it was at Newhall, South Derbyshire and in 2000, it was in Appleby Parva, Leicestershire.
The centre of population of the entire island of Ireland is located near Kilcock, County Kildare. This is significantly further east than the Geographical centre of Ireland, reflecting the disproportionately large cities of the east of the island (Belfast and Dublin). The centre of population of the Republic of Ireland is located southwest of Edenderry, County Offaly.
The centroid of population of Japan is in Gifu Prefecture, almost directly north of Nagoya city, and has been moving east-southeast for the past few decades. More recently, the only large regions in Japan with significant population growth have been in Greater Nagoya and Greater Tokyo.
In June 2008, New Zealand's median centre of population was located near Taharoa, around 100 km (65 mi) southwest of Hamilton on the North Island's west coast. In 1900 it was near Nelson and has been moving steadily north ever since.
The demographical center of Sweden (using the median center definition) is Hjortkvarn in Hallsberg Municipality, Örebro county. Between the 1989 and 2007 census the point moved a few kilometres to the south, due to a decreasing population in northern Sweden and immigration to the south.
The mean center of the United States population (using the centroid definition) has been calculated for each U.S. Census since 1790. Over the last two centuries, it has progressed westward and, since 1930, southwesterly, reflecting population drift. For example, in 2010, the mean center was located near Plato, Missouri, in the south-central part of the state, whereas, in 1790, it was in Kent County, Maryland, 47 miles (76 km) east-northeast of the then-new federal capital, Washington, D.C.
The United States Census of 1820 was the fourth Census conducted in the United States. It was conducted on August 7, 1820. The 1820 Census included six new states: Louisiana, Indiana, Mississippi, Illinois, Alabama and Maine. There has been a district wide loss of 1820 Census records for Arkansas Territory, Missouri Territory and New Jersey, however.
The total population was determined to be 9,638,453, of which 1,538,022 were slaves. The center of population was about 120 miles (193 km) west-northwest of Washington in Hardy County, Virginia (now in West Virginia).
This was the first census in which a state recorded a population of over one million – New York and Pennsylvania – as well as the first in which a city recorded a population of over 100,000 – New York. It was also the first census in which Baltimore was ranked as the country's second-most populous city.1830 United States Census
The United States Census of 1830, the fifth census undertaken in the United States, was conducted on June 1, 1830. The only loss of census records for 1830 involved some countywide losses in Massachusetts, Maryland, and Mississippi.
It determined the population of the 24 states to be 12,866,020, of which 2,009,043 were slaves. The center of population was about 170 miles (274 km) west of Washington, D.C. in present-day Grant County, West Virginia.
This was the first census in which a city – New York – recorded a population of over 200,000.1840 United States Census
The United States Census of 1840 was the sixth census of the United States. Conducted by the Census Office on June 1, 1840, it determined the resident population of the United States to be 17,069,453 — an increase of 32.7 percent over the 12,866,020 persons enumerated during the 1830 Census. The total population included 2,487,355 slaves. In 1840, the center of population was about 260 miles (418 km) west of Washington, near Weston, Virginia.
This was the first census in which:
A state recorded a population of over two million (New York)
A city recorded a population of over 300,000 (New York)
Multiple cities recorded populations of over 100,000 (New York, Baltimore, and New Orleans)Boone County, Indiana
Boone County is a county located in the U.S. state of Indiana. As of 2010, the population was 56,640. The county seat is Lebanon. Indiana's center of population is located in eastern Boone County, just northwest of the town of Sheridan in neighboring Hamilton County.Conway County, Arkansas
Conway County is a county located in the U.S. state of Arkansas. As of the 2010 census, the population was 21,273. The county seat is Morrilton. The county was formed on October 20, 1825, from a portion of Pulaski County and named for Henry Wharton Conway who was the territorial delegate to the U.S. Congress.
In 2010, the center of population of Arkansas was located in Conway County, near the city of Plumerville.Gassaway, West Virginia
Gassaway is a town in Braxton County, West Virginia, in the United States. The population was 908 at the 2010 census. Gassaway was incorporated in 1905 and named for Henry Gassaway Davis, the Democratic Party's nominee for Vice President of the United States in 1904. The center of population of West Virginia is located approximately 7 miles (11 km) north of Gassaway.Jefferson County, Colorado
Jefferson County (Jeffco) is one of the 64 counties in the U.S. state of Colorado. As of the 2010 census, the population was 534,543, making it the fourth-most populous county in Colorado. The county seat is Golden, and the most populous city is Lakewood.
Jefferson County is included in the Denver-Aurora-Lakewood, CO Metropolitan Statistical Area. Located along the Front Range of the Rocky Mountains, Jefferson County is adjacent to the state capital of Denver.
In 2010, the center of population of Colorado was located in Jefferson County.The county's slogan is the "Gateway to the Rocky Mountains", and it is commonly nicknamed Jeffco. The name Jeffco is incorporated in the name of the Jeffco School District, the Jeffco Business Center Metropolitan District No. 1, and several businesses located in Jefferson County. Jeffco is also incorporated in the unofficial monikers of many Jefferson County agencies. The Rocky Mountain Metropolitan Airport operated by Jefferson County was previously known as the Jeffco Airport.
A major employer in Jefferson County is the large Coors Brewing Company in Golden. Also, the state-supported Colorado School of Mines is located in Jefferson County, offering programs in STEM topics such as mining, geology, chemistry, and engineering.King County, Washington
King County is a county located in the U.S. state of Washington. The population was 2,188,649 in the 2017 census estimate. King is the most populous county in Washington, and the 13th-most populous in the United States. The county seat is Seattle, which is the state's largest city.
King County is one of three Washington counties that are included in the Seattle–Tacoma–Bellevue metropolitan statistical area. (The others are Snohomish County to the north, and Pierce County to the south.) About two-thirds of King County's population lives in Seattle's suburbs.Lincoln County, Oklahoma
Lincoln County is a county in eastern Central Oklahoma. As of the 2010 census, the population was 34,273. Its county seat is Chandler.Lincoln County is part of the Oklahoma City, OK Metropolitan Statistical Area.In 2010, the center of population of Oklahoma was in Lincoln County, near the town of Sparks.List of counties in Tennessee
This is a list of the 95 counties in the State of Tennessee. A county is a local level of government smaller than a state and typically larger than a city or town, in a U.S. state or territory.
As of 2010, Shelby County was both Tennessee's most populous county, with 927,644 residents, and the largest county in area, covering an area of 755 sq mi (1,955 km2). The least populous county was Pickett County (4,945) and the smallest in area was Trousdale County, covering 114 sq mi (295 km2). As of the same year, Davidson County, in which the capital Nashville is located, covers 502 sq mi (1,300 km2) with a population of 569,891. The population of the state of Tennessee as of the 2000 census was 5,689,283 in an area of 42,169 sq mi (109,217 km2). The oldest county is Washington County, founded in 1777. The most recently formed county is Chester County (1879).According to the 2000 census, the center of population for Tennessee was located at 35.795862°N 86.397772°W / 35.795862; -86.397772, 2.5 mi (4.0 km) south of Murfreesboro in Rutherford County. The center of population pinpoints the location at which the population of the state, as placed on a map of the state where they reside, would balance out the map. The geographic center, the point where the map of Tennessee would balance without the population, is located 5 mi (8 km) northeast of Murfreesboro. In 1976, the Rutherford County Historical Society marked the geographic center of Tennessee with an obelisk.Some of the counties were formed in part or completely from lands previously controlled by American Indians. The "Indian lands" were territories that American Indians had occupied from pre-Columbian times and to which they were granted the legal right of occupancy in an act of the United States government. In cases where counties had been formed from that territory, the legal right of American Indian occupancy was revoked in a federal act prior to the formal establishment of the county. For Tennessee, ten treaties were negotiated between 1770 and 1835, defining the areas assigned to European settlers and to American Indians, regulating the right of occupancy regarding the lands. The remaining indigenous population was eventually removed from Tennessee to what became the state of Oklahoma.The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify counties, is provided with each entry. FIPS codes are five-digit numbers; for Tennessee the codes start with 47 and are completed with the three-digit county code. The FIPS code for each county in the table links to census data for that county.Meagher County, Montana
Meagher County (pronounced Marr) is a county located in the U.S. state of Montana. As of the 2010 United States Census, the population was 1,891. Its county seat is White Sulphur Springs.According to the US Census Bureau, the 2010 center of population of Montana is located in Meagher County at 46.78°N 111.3°W / 46.78; -111.3Mean center of the United States population
The mean center of the United States population is determined by the United States Census Bureau from the results of each national census. The Bureau defines it as follows:
The concept of the center of population as used by the U.S. Census Bureau is that of a balance point. The center of population is the point at which an imaginary, weightless, rigid, and flat (no elevation effects) surface representation of the 50 states (or 48 conterminous states for calculations made prior to 1960) and the District of Columbia would balance if weights of identical size were placed on it so that each weight represented the location on one person. More specifically, this calculation is called the mean center of population.
After moving roughly 600 mi (966 km) west by south during the 19th century, the shift in the mean center of population during the 20th century was less pronounced, moving 324 mi (521 km) west and 101 mi (163 km) south. Nearly 79% of the overall southerly movement happened between 1950 and 2000. Given the strong pull of Texas, Florida, and the Western US, the population center would be heading towards and one day entering Oklahoma.Northern Kentucky
Northern Kentucky is the name often given to the northernmost (most typically the three northernmost) counties in Kentucky (Boone, Kenton, Campbell, shown in red on the map). Gallatin, Grant, Pendleton, and Bracken counties (highlighted in pink on the map) are often grouped with the aforementioned and are officially part of the Cincinnati metropolitan area, and are sometimes included in definitions of "Northern Kentucky." Historically, Trimble, Mason, and Lewis counties have also been included in "Northern Kentucky."
The three northernmost counties of Kentucky each has at least one major center of population: Florence in Boone County; Covington, Erlanger, and Independence in Kenton County; and Newport, Fort Thomas, and Alexandria in Campbell County. Immediately on the northern side of the Ohio River from Covington and Newport is Cincinnati, Ohio. However, the entire core region is relatively densely populated, with these cities surrounded by many smaller towns which have little other than a city limit sign between them. The periphery of Boone, Kenton, and Campbell counties, namely the western half of Boone County, and southernmost parts of all three of the core counties, are still primarily rural in nature. The area, primarily the three northernmost counties, has a high amount of German heritage and moderate Irish heritage, being across the river from Cincinnati. The four outer counties are still primarily rural. Combined with the southeast corner of Indiana, and Southwestern Ohio, all seven counties are a part of the Greater Cincinnati area, which has a population over two million.
The area was served by ferry service across the Ohio River until the completion of the John A. Roebling Suspension Bridge (prototype of the famous Brooklyn Bridge) in 1866, whereupon land values in the areas near the river quadrupled overnight.
Beginning in the 1970s, many factors combined to create major growth. The proximity to Cincinnati, the completion of I-75, the nexus of rail service and river traffic, creation of several industrial parks, and the growth of Cincinnati/Northern Kentucky International Airport (located near Hebron in northeastern Boone County near the Kenton County line) drew many industries into the area. Its geographically central location (within 800 miles (1,300 km) of 80% of the US population) makes it ideal for distribution centers, and those shipping all over the country.
In addition to location, the Northern Kentucky area hosts several organizations which strive to enhance the quality of life and the local economy. These organizations include: The Northern Kentucky Chamber of Commerce (NKY Chamber), the Northern Kentucky Tri-County Economic Development Corporation (NKY Tri-ED), Vision 2015, Southbank Partners, the Catalytic Fund, the Northern Kentucky One Stop, and the Kentucky Cabinet for Economic Development (KCED). The primary airport (CVG) serving Cincinnati is located in Northern Kentucky.Pembroke, New Hampshire
Pembroke is a town in Merrimack County, New Hampshire, United States. The population was 7,115 at the 2010 census. Pembroke includes part of the village of Suncook. The center of population of New Hampshire is located in Pembroke.Pike County, Indiana
Pike County is a county located in the southwest portion of the U.S. state of Indiana. As of 2010, the population was 12,845. The county seat is Petersburg. It contains the geographic point representing median center of population of the United States.Pike County is part of the Jasper Micropolitan Statistical Area.Texas County, Missouri
Texas County is a county located in the southern portion of the U.S. state of Missouri. As of the 2010 census, the population was 26,008. Its county seat is Houston. The county was organized in 1843 as Ashley County, changing its name in 1845 to Texas, after the Republic of Texas.
The 2010 U.S. Census indicates that it is the center of population for the United States.Townsend, Delaware
Townsend is a town in New Castle County, Delaware, United States. The population was 2,049 at the 2010 census, an increase of 492.2% from 2000. The center of population of Delaware is located in Townsend.Two Harbors, California
Two Harbors, colloquially known as "The Isthmus", is a small unincorporated community island village on Santa Catalina Island, California, with a population of 298 (Census of 2000). It is the second center of population on the island, besides the city of Avalon. It is mainly a resort village. It has only one restaurant, one hotel and one general store. The village has about 150 permanent residents who live on the isthmus year-round. One notable feature was the one-room schoolhouse which closed in 2014.Washington County, Kentucky
Washington County is a county located in the U.S. state of Kentucky. As of the 2010 census, the population was 11,717. Its county seat is Springfield. The county is named for George Washington.Washington County was the first county formed in the Commonwealth of Kentucky when it reached statehood, and the sixteenth county formed. The center of population of Kentucky is located in Washington County, in the city of Willisburg.The county is dry, meaning that the sale of alcohol is prohibited, but it contains the "wet" city of Springfield, where retail alcohol sales are allowed. This classifies the jurisdiction as a moist county. Three wineries operate in the county and are licensed separately to sell to the public. Jacob Beam, founder of Jim Beam whiskey, sold his first barrel of whiskey in Washington County.