Neither Tokyo nor Shanghai. Cairo-Alexandria-Luxor, in Egypt, is the world's largest megacity, with 63.5 million inhabitants
What would be the biggest city in the world? Whoever thought about Tokyo or Shanghai is wrong. According to the results of a new algorithm developed by Brazilian researchers and an Argentine, the largest city in the world is the conurbation that unites the cities of Alexandria, Cairo and Luxor in Egypt with 63.5 million inhabitants. In second place is Dhaka, the capital of Bangladesh (48.4 million), and third is the Guangzhou-Macau-Hong Kong conurbation in China, with 44.4 million inhabitants.
From the demographic point of view, the legal definition of a city is the district that houses the municipality. Nowadays, when demographic expansion and the explosive growth of cities mean that, for the first time in human history, half the world population lives in urban centers, that definition of city seems too simplistic.
"People still do not know how to define a city very well. There is a big problem in this respect: one way to define cities is to think of groups of people, but the group may eventually be larger than the administrative boundaries of the city," says physicist Erneson Alves de Oliveira, of the Laboratory of Knowledge Engineering, University of Fortaleza (Unifor), at Fortaleza, Brazil. "A clear way to visualize this is the nighttime images of continents made by satellites. The large clusters of cities are those spots of light that are spreading on the black background, from a large metropolis, and connecting to others urban centers."
According to Oliveira, a modern view of cities establishes that they can be defined by the interactions between various types of networks, from infrastructure networks to social networks. "In recent years, a growing number of studies have been proposed to define cities through consistent mathematical models to investigate urban indicators at inter- and intra-city scales, in order to shed some light on the problems faced by decision makers."
This is exactly what Oliveira and Vasco Furtado, of Unifor, along with José Soares de Andrade Júnior, from the Physics Department of the Federal University of Ceará, and Hernán Alejandro Makse, of City College of New York. They created a new algorithm to quantify cities that takes into account both demographic and infrastructure data, as well as social and cultural data specific to the region, the country and the continent where the metropolis analyzed are located. The paper "A World Model for Urban Settlement Boundaries" was published in the British scientific journal Royal Society Open Science.
"What we propose a worldwide model to define urban settlements beyond their administrative boundaries," says Oliveira. "This is done through a bottom-up approach that takes into account geographical biases intrinsically associated with most societies around the world. These data directly reflect the regional dynamics of growth as well as the dynamics of population distribution in different continents."
As an example of such relationships, consider a city with population size X that consumes an amount of water Y. If population doubles (2X), water consumption will also double (2Y). Water consumption is an urban indicator that observes a ratio of proportionality (isometric) to population increase.
There are, however, urban indicators that observe disproportionate relations (so-called allometric relations). Such as the number of gas stations. A city of population X has Y gas stations. It is clear that if the population doubles (2X), the number of stations will not need to double to keep up with the increased demand for fuel. The number of stations needed to supply the city 2X is less than 2Y. Here, what comes into play is the so-called "economy of scale".
The new algorithm to estimate the size of cities created by Oliveira and colleagues aims to provide a more accurate result of the size of cities for the correct inference of the urban indicators.
According to Oliveira, there are hierarchical mechanisms behind the growth and innovation of urban settlements. These mechanisms are governed by a combination of general measures such as population and area of each city, and intrinsic factors that are region-specific such as topographical heterogeneity, political and economic issues, and cultural customs and traditions. "In other words, if political turmoil or economic recession plagues a metropolis for a long time, all of its satellites are affected too, i.e. the entire region ruled by the metropolis will be negatively impacted."
The public administrator needs this information to decide how best to allocate the resources available to him to invest in infrastructure, education, transportation, security and health. All of these public policies are based on some urban indicators, which obviously can change a lot when you consider only one city, or a metropolitan region, or an even greater conurbation.
 |
| The pyramids of Giza can be seen in the distance. Cairo, Egypt (copyright Dennis Jarvis) |
After all, what is a city?
Defining what a city is is no easy task. If the criterion used is the total number of inhabitants living in a metropolitan area, then the largest metropolis in the world is Tokyo with 37.9 million inhabitants, followed by Jakarta in Indonesia with 31.9 million and Cairo in Egypt in third (27.3 million). Under this criterion, São Paulo is ranked 10th, with 20.8 million, and among the ten largest cities there are two Chinese (Shanghai and Beijing), two Indian (Delhi and Mumbai), Mexico City and Seoul, in South Korea.
But there are other ways of quantifying cities. When you take into account the individual data of each county, the largest city in the world is Shanghai with 17.8 million inhabitants. In this ranking São Paulo occupies the 7th place, with 12.1 million, while Tokyo falls to 16th, with 9.07 million.
Instead of using an absolute criterion as the number of inhabitants, one can also define cities by relative criteria, such as population density, that is, the number of people per square kilometer (km2). Thus, the largest city in the world becomes Dhaka, the capital of Bangladesh, with 16 million inhabitants and population density of 45,700 people per km2, and the second largest city is Mogadishu, Somalia, which has 2.45 million inhabitants, but population density of 26.8 thousand people per km2. According to this criterion, the other eight of the ten largest cities in the world are in China (Hong Kong and Macau), India (Mumbai, Surat and Vijayawada), Pakistan (Hyderabad and Karachi), and Raqqa in Syria.
The size of a city can still be defined according to its urban area. In this case, the largest metropolis in the world would be New York, whose population of 21.5 million occupies an area of 11.8 thousand km2, which is 7.6 times greater than the urban area of the City of São Paulo.
There are so many possible criteria for defining cities that the authors of this paper set out a daring challenge: to build a mathematical model that would be powerful enough to define the largest cities on the planet.
"Our model is called the "city local clustering algorithm" (CLCA). It was built from a pre-existing model, the "city clustering algorithm" (CCA), which also defines cities in addition to their administrative boundaries for non-continental cases, using the notion of spatial contiguity of urban settlements and the level of commutation between them," says Oliveira. "Thus, the CCA is defined for discrete or continuous landscapes by two parameters: a population density threshold and a distance threshold. These parameters describe the populated areas and the commuting distance between areas, respectively.
The researchers' study used data from Columbia University's Socioeconomic Data and Application Center. to apply the CLCA algorithm to a single global dataset. Such a dataset is a compilation of gridded census and satellite data for the populations of urban and rural areas of 232 countries in the year 2000.
 |
| Alexandria, Egypt, satellite image |
Cairo-Alexandria-Luxor
"According to our results, the largest cities in the world are not in line with what was recently reported by the United Nations," says Oliveira. "We found that the largest city in the world is an agglomeration of several small settlements close to each other, connecting three large settlements: Alexandria, Cairo and Luxor."
Alexandria and Cairo are neighboring cities. It is interesting to note that Luxor, also located on the banks of the Nile River like Cairo, is 650 kilometers away from the other two cities. That is, according to the algorithm created by the researchers the 650 kilometers of banks of the Nile that connect Luxor to Cairo form a single urban entity.
"It is well known that almost the entire population of Egypt lives in a strip along the Nile, in the Nile delta and in the Suez Canal, which together corresponds to 4% of the total area of Egypt. It is where there is arable land to produce food," explains Oliveira.
"The river and delta regions are composed by some large cities and a lot of small villages, making them extremely dense. Therefore, our results raise the hypothesis that the cities and villages across the Nile can be seen as a kind of ‘megacity’, despite spatially non-contiguous, due to the socioeconomic relation, reflected in the high commuting levels, among close subregions."
Press contact:
Luiz Carlos de Carvalho
CONTACT WITH THE AUTHOR:
Prof. Dr. Erneson Alves de Oliveira
Laboratório de Engenharia do Conhecimento
Universidade de Fortaleza (Unifor)
Fortaleza-CE, Brazil
Phone: (55 85) 3477-3079
Mobile: (55 85) 98118-0407
e-mail: erneson@fisica.ufc.br
Press contact:
Luiz Carlos de Carvalho
Trabalho: (55 85) 3477-3840
Celular e whatsapp: (55 85) 99820-7654
e-mail: luizcarlosdecarvalho@gmail.com
SCIENTIFIC REFERENCE:
Oliveira EA, Furtado V, Andrade JS, Makse HA. 2018 A worldwide model for boundaries of urban settlements. R. Soc. open sci. 5: 180468. http://dx.doi.org/10.1098/rsos.180468
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0)
Comentários
Postar um comentário