By Matt Burdett, 1 March 2018
On this page, we look at the planned and spontaneous growth processes of cities.
- The Forum, Rome, Italy: This ancient city’s central area was planned, but the population growth around it was not. Source: By the author.
Causes of growth
Settlements grow and become cities for three reasons:
- A settlement is reclassified as a city
- Natural increase (birth rate is higher than death rate) causing the settlement to grow into a city
- Migration into a settlement makes it grow into a city
These three issues are shown in the diagram below from the United Nations Population Division. The diagram shows how settlements grow in a variety of ways.
- Methodologies of classifying urban areas. Source: UNPD, 2018.
Settlements are rarely reclassified as cities unless they have already grown in population size; and in general, natural increase in urban areas is lower than in rural areas. Therefore, in-migration is the most common cause for city growth. The question is: why do people migrate to cities?
Standard migration models such as Lee’s model (below) identify the balance between push and pull factors. This balance is the cause of the migration. In general, cities have historically had more pull factors, resulting in in-migration.
- A model of migration. Source: Lee, 1966.
However, these models do not explain why the location of the city is so good compared to other settlements that people could move to. The rest of this page explains why some settlements are more popular for in-migration than others and grow into cities.
Spontaneous city growth
Spontaneous city growth usually refers to growth that isn’t planned, especially the ‘footprint’ of the urban area. (No government has total control over population movements and growth rates; therefore there is an element of spontaneous population growth in all cities.)
Central Place Theory
Imagine a location in which settlements are close together, like in the diagram below. Some functions of settlements are too specialised to happen in each settlement, and so will only happen in one of the settlements. These functions are ‘high order’ functions – things like having the main government buildings, or the headquarters of banks, or the main shopping district selling specialized products for the entire area. This means that one settlement will grow bigger than the others. Which settlement would be most likely to grow?
In the real world, the answer would depend on lots of factors – which one has the best water supply, the best transport links, the lowest chance of flooding and so on. But, imagine that each settlement is identical. Which would be the most likely now?
The settlement in the centre will be the largest, because it is the easiest to access from all the other settlements. This is the basic feature of ‘Central Place Theory’. Now, imagine that these are not the only settlements – in fact, there are many more settlements. They will also be arranged with central places as shown below.
In the Central Place Theory created in 1933 by Walter Christaller, there is an ever-overlapping set of central places. Christaller was a German Geographer who was studying places in the south of Germany. He identified that urban settlements can be placed into a hierarchy and that the spacing between each settlement appeared to be uniform. This is commonly shown in diagrams using a series of hexagons, as shown in the diagram below. Major settlements are represented by the large pink dots; the next largest by smaller purple dots, and even smaller settlements by blue dots.
- Central Place Theory, in diagram form. Click the image to go to the original animated version. Source: Avenafatua, 2007.
Each settlement is separated from the other settlements in its category by the same distance, resulting in the hexagon shapes showing how each settlement is ‘central’ within the hexagon. Settlements within each hexagon of the next largest settlement will use that larger settlement to access services and markets.
This is known as the ‘market principle’. It explains why some settlements grow and others don’t. If two settlements are close together, only one of them will become the ‘central place’: the competition between the two settlements will result in one winning and becoming larger, because people from the other settlements in the area will gather towards it. The other settlement will remain small and not grow.
Christaller’s model helps to explain why some settlements grow, even without any deliberate attempt at planning.
In 1970, James Vance published his book ‘The merchant’s world: the geography of wholesaling’ in which he suggested how transport networks develop over time. His ideas have also been used to give a more practical – meaning less theoretical – view of why some settlements grow.
He based his ideas on a series of historical events that took place between Europe and North America, starting with the earliest stages of colonisation. In his model, the settlement distribution in the eastern seaboard of the United States is dependent not on central places but on transport routes. Settlements needed to trade through coastal ports, so transport networks developed in an east-west pattern to provide easy access, which in turn allowed these settlements to grow even more.
- Vance’s 1970 ‘mercantile model’ of transport networks, which can also be used to explain settlement patterns. Source; Raghav, n.d.
Over time, north-south transport links were also developed, but by this point the settlement pattern was set and is maintained to this day. (Look at a map of the north-east USA, and it is clear that Boston, New York, Philadelphia and other settlements do not conform to an obvious central place pattern.)
Planned city growth
Most governments today do not allow settlements to grow spontaneously; although they might not control the population movement and growth directly, they do control the way in which land is allowed to be used. This means that governments do plan the growth of settlements to an extent.
Most governments in HICs and MICs enforce laws that state whether new building is allowed or not. ‘Planning permission’ is often granted on the edge of settlements to accommodate the increasing population. This permission is often given for a few hundred homes at a time.
In LICs, the laws may be present but it is harder to enforce because of a lack of funds and, often, greater pressure from rural to urban migration. In all countries there are areas where new building is rarely allowed, such as in national parks.
Sometimes there are much larger urban projects, such as new towns, edge cities and planned city extensions.
New Towns are settlements that have been created ‘brand new’ and do not have a history as a large settlement. They are entirely planned.
The New Town movement began in Europe in the early 20th century as existing cities became crowded and polluted. Entirely new settlements were designed on the outskirts of cities such as London. They were often designed with attracted green environments (trees, parks and so on) with wide streets and good transport links. After World War Two, New Towns became increasingly popular in the United Kingdom as a way to rehouse the large numbers of people whose homes had been destroyed by bombing. Examples include Welwyn Garden City, Stevenage and Milton Keynes.
New Towns also exist in other parts of the world. Town such as Olgiata near Rome in Italy, Ma On Shan in Hong Kong and Barra da Tijuca near Rio de Janeiro in Brazil have all been developed with decisive government planning.
Planned city extensions
As cities grow, it is important to plan the expansion. A planned city expansion takes place where the authorities deliberately allow an area to grow, and ensure that it contains suitable transport, energy, water and sanitation infrastructure, as well as the ‘soft’ infrastructure of healthcare, education and so on.
The United Nations Habitat agency’s mission is “to promote socially and environmentally sustainable human settlements development and the achievement of adequate shelter for all” (UN Habitat, 2012). UN Habitat’s analysis of historic planned city expansions shows that successful planned city extensions often involve the following (UN Habitat, 2015):
- Initial planning on a street grid system
- Planning needs to be flexible and change according to how the city then grows
- Some regulation is needed to prevent speculation (people buying land in the hope that it rises in value)
- The regulations should include provision for mixed-use land use, by allowing some mixing of residential, commercial and leisure spaces
- Variety is key interesting, vibrant cities arise from departing from a planned grid system occasionally and including parks, diagonal streets on the grid, and allowing natural topographical features such as hills, rivers and coastlines to become main features of the urban area
Avenafatua, 2007. Illustration of Christaller’s central place theory. https://en.wikipedia.org/wiki/Central_place_theory#/media/File:Christaller%27s_central_place_theory_animation.gif Accessed 1 March 2019.
Lee, 1966. A Theory of Migration. In Demography Vol. 3, No. 1 (1966), pp. 47-57 http://www.jstor.org/stable/2060063 Accessed 10 May 2018.
UNPD, 2018. World Urbanization Prospects 2018: Methodology: Definition Issues. https://esa.un.org/unpd/wup/General/DefinitionIssues.aspx Accessed 19 May 2018.
Raghav, n.d. 4 Models of Transport Development (Explained With Diagram). http://www.geographynotes.com/articles/4-models-of-transport-development-explained-with-diagram/60 Accessed 1 March 2019.
Vance, J.E., 1970. The merchant’s world: the geography of wholesaling. Prentice Hall. [No online access]
UN Habitat, 2012. UN-Habitat at a glance. https://unhabitat.org/un-habitat-at-a-glance/ Accessed 1 March 2019.
UN Habitat, 2015. Planned City Extensions: Analysis Of Historical Examples. https://unhabitat.org/books/planned-city-extensions-analysis-of-historical-examples/ Accessed 1 March 2019.
Growth processes of cities: Learning activities
- What are the three ways in which a settlement can become a ‘city’? 
- Explain why in-migration is the dominant form of settlement growth. 
- Define ‘spontaneous settlement growth’. 
- Briefly outline Central Place Theory. 
- Briefly outline Vance’s mercantile model. 
- Define ‘planned city growth’. 
- Explain why new towns were needed after World War Two. 
- Describe the main features of planned city extensions. 
- Outline the main features of successful planned city extensions. 
- “No government can plan the growth of settlements.” Discuss this statement. 
Look at https://unhabitat.org/books/planned-city-extensions-analysis-of-historical-examples/ and identify three examples of planned city extensions from different continents. Decide which is the most successful planned city expansion and explain the reasons for your decision.
Investigate the assumptions of Christaller’s theory and assess how well it works for your area. An excellent source of information about Christaller’s Central Place Theory is found at https://planningtank.com/settlement-geography/central-place-theory-walter-christaller
© Matthew Burdett, 2019. All rights reserved.
All secondary material on this site is clearly referenced and may be subject to copyright restrictions by the original authors. All original material on this page is subject to copyright.