With an unprecedented urbanisation rate, cities of the 21st century are facing a new set of challenges. Some cities face basic resource scarcity or are required to constantly adapt their infrastructures because of high population growth. Given the high number of coastal cities, many are, or will be, impacted by the effects of climate change. But whilst there are reasons to be worried by these new challenges, they also represent an infinite potential for technological innovation in order to be solved and adapt cities to a changing world. One of these challenges is urban land-constraint. Urban land scarcity can be defined as a situation that appears when cities do not have enough land to further build infrastructures and sustain its growth. Typically, such land is constrained as it is limited to the Earth’s total land mass (~30% of the Earth’s surface). Considering that an estimated 3% of this land mass is occupied by urban areas,  the challenge of urban land scarcity may seem relative compared to other more urgent issues, but remains an interesting one that deserves our attention nonetheless.
It is important to differentiate two main types of urban land constraints: the ones caused by geographical or natural factors and those artificially caused by urban regulations.
Certain cities are indeed limited by either natural or political borders and are the most obvious examples that come to mind when thinking of urban land constraint. New York City’s Manhattan borough, being an island, is therefore de facto land constrained and its potential expansion is limited. Of course, New York City, not being limited to Manhattan island, can expand throughout its five boroughs and even beyond, but Manhattan itself will always be limited to its natural borders. As for urban land-scarcity being caused by political borders, a good example is Monaco, as it is surrounded by France on three sides and the Mediterranean Sea on the fourth, which makes its expansion practically impossible.
However, while geography may play a rather obvious role in making a city land-constrained or not, this is also the case of legislations and urban regulations. Obviously, a city cannot only possess housing units as it needs other infrastructures such as parks and other public services, to insure the highest possible quality of life for its citizens. Manhattan has the obvious example of Central Park, which represents 6% of Manhattan’s land area,  yet plays a vital role in the Manhattanites’s wellbeing and certainly compensates for the lack of green areas in denser neighbourhoods on the island. But Central Park also represents an important landmass that cannot be built upon, hence reinforcing this idea of land-scarcity in Manhattan. Furthermore, whilst Manhattan is often considered as land-constrained, most of the area between Lower and Midtown Manhattan is home to low-rise building which are protected by New York’s urban planning and laws.  As a result, it is fair to say that geography does lay the basis for urban land-scarcities, but urban planning and legislations are often what lead to the development and spread of it.
Urban land-scarcity leads to problems such as high population density. For instance, Manhattan has the highest density of any county in the United States with around 70,000 inhabitants per square mile.  Additionally, many city-states such as Monaco, Hong Kong, Macau or Singapore have some of the highest densities in the world (e.g. Hong Kong’s Mong Kok neighbourhood).  While it doesn’t always represent an issue, sometimes it can lead to overcrowding and congestions as well as an overall lower quality of life due to a lack of green spaces and parks, for example.
Another urban issue partly caused by land constraint is high real estate prices. If an area has no more land to build infrastructure such as housing blocks or offices, but that demand continues to grow, typically real estate prices drastically increase. This seems true when looking at real estate prices and the fact that New York, Hong Kong, Monaco and Singapore are all in the top 10 of the most expensive cities worldwide for housing prices.  Of course, whilst this may be a reason in explaining the height of home prices, it certainly is not the only explanation as the economic and cultural attractiveness of these cities equally has to be considered, as well as the housing market’s stability in those cities and the opportunities of investing in them. Nonetheless, for cities such as Singapore, Hong Kong or Monaco, the issue of land scarcity certainly plays a role in ever increasing real estate prices. In Hong Kong, the case of the “cage homes” is a symbol of its grave housing crisis with rents so high that some can only afford to live in apartments the size of a bed.
One of the evident solutions, when a city has no more room to expand and increasing demand is pressuring the housing system, is to build upwards. This concept is not new and cities such as Singapore, Hong Kong or Monaco, all land scarce, have had no other choice than to constantly build high rise residences to accommodate growing populations. Hong Kong, with 1,386 skyscrapers, has the highest numbers of skyscrapers of any city in the world.  This has led to a high population density which, as mentioned earlier, has its own consequences. However, whilst building upwards might greatly help land-scarce cities for a while, it is not a long-term solution as technologically we can only build so high, not to mention that this hinders a set of other urban challenges such as flight-paths or other urban regulations. For instance, the Singapore Business District suffers from a maximum height limit of 280m due to the proximity with some of the Singaporean army air bases. 
Additionally, land-constrained cities often turn to land reclamation, which is the process of filling previously unusable lands such as wetlands, or simply creating new land in the sea in order to enlarge their territories. According to government statistics, Macau has grown about 165% in land territory since 1912.  Similarly, it is estimated that Singapore has increased in landmass by between 20 and 25% since 1965.  A prime example of this land reclamation is the whole Marina Bay area, which is now home to the Marina Bay Sands hotel and Gardens by the Bay, which have become some of Singapore’s most famous tourist attractions, demonstrating the vitality of land reclamation for cities like Singapore. For similar purposes, Hong Kong plans to build a whole new island that, once completed, will be home to approximately 700,000 inhabitants with the hope to fix Hong Kong’s housing crisis. 
The final major solution to urban scarcity is infrastructural development. Whilst new skyscrapers or high-rise buildings can be considered as infrastructures too, what is particularly meant here is transport infrastructures. Roads, (underground) railways, bridges, and so on, allow for a better connectivity between different areas of a city and can limit the effects of urban scarcity. For instance, with the new Hong Kong-Zhuhai-Macau Bridge (HZMB), Hong Kong’s government hopes that with new regulations allowing Hong Kong citizens to move back and forth between the city and China, citizens of the SAR will buy a home somewhere else in the Pearl River Delta and regularly commute to Hong Kong. This presents a potential remedy to the city’s housing crisis and future need for land reclamation. Infrastructural development is what allows a city to become expansive rather than “expensive”. One could hope that projects such as the American Hyperloop One project will allow for greater commutes and repartition of populations, virtually eliminating the issue of urban land-scarcity.
All these “solutions” come at a cost and aren’t always ideal. The construction of higher buildings doesn’t necessarily fix housing crises. Brand-new skyscrapers are being built in the centre of cities such as New York to apparently tackle these cities housing shortage or high real-estate prices. However, it is debatable whether these new high-rise residential buildings actually help or if they mainly represent an investment opportunity for wealthy people who may or may not intend to live in these apartments. Certain cities such as New York are experiencing a rise in construction of new slender skyscrapers. Given the high cost of land in areas such as Manhattan, some developers have decided to build highly luxurious residential buildings, like the case of what is becoming known as “Billionaire’s row” in the southern tip of Central Park.  Not only does this issue potentially fail to resolve New York’s housing shortage, it can also drive up real estate prices in surrounding blocks, given the luxury standards of these new buildings.
Land reclamations are not perfect either. While costly, they are often done by cities that have the means to pay for them. However, the necessity of land reclamations or their impact on the environment can sometimes be questionable. As mentioned, Hong Kong’s government was planning to build a new artificial island to house some 700,000 people. And while the necessity to provide affordable housing for current and future residents of the city is clear, the actual decision of building a brand-new artificial island is questionable. There has always been this idea that the city was land constrained because of its border with China and its numerous mountains, making construction practically impossible. This led to many skyscrapers having to be built and home prices soaring. Yet while some of this is indeed true, the fact is that less than a quarter of Hong Kong’s landmass is actually built-up and less than 7% of that is used for housing.  A part from country parks, there is still a lot of land left for building affordable housing. Most of the flat farmlands that border the city of Shenzhen are abandoned and some of it is owned by developers who see no incentive to develop these lands because it can enable them to control real-estate prices in the city.  When acknowledging that Hong Kong still has a lot of land available for developing despite the recurring idea that Hong Kong is land constrained, it makes the project of creating a gigantic artificial island seem irrational, especially given the environmental impact that it could have. This impact should also be considered for any future land reclamation, given the considerable amount of resources, mainly sand, that need to be transported and the disruption to the local ecosystem that it causes.
The issue of Urban land constraint remains to evaluate how much of it is caused by geographical factors compared to urban regulations, with Hong Kong as prime example as the idea of its land limitation is not new, however, not entirely true either. Nonetheless, for those that are land-constrained for a reason or another, there are various possible solutions such as building higher or reclaiming land. It is true that none of these are absolutely perfect but remain interesting options nonetheless. Additionally, it must be said that practically all the cities mentioned in this article, whether Monaco, Singapore or Hong Kong, are very wealthy cities that have the money to tackle the issue of land-constraint. Unfortunately, not every city that suffers from this issue disposes of the same amount of resources. Cities such as Cairo (Egypt) or Dhaka (Bangladesh), which are experiencing important population growth, face the risk of expanding in agricultural land that is vital for providing food security, hence creating a dilemma between agricultural or urban land-scarcity. Another extreme example of land scarcity would be Malé (Maldives), where the whole island has been built up, with little to no room to further expand.  All in all, whether a rich or poor city, the challenge of land-constraint will become ever more present as grand-scale urbanisation continues in the decades to come.
Louis HOBBS MARTIN
Louis is a second year Ba. International Relations student at King’s College London. He is an editor for Sensus as well as manager of its social media.
His particular interests lay in the region of China and South-East Asia. He also writes for the KCL International Relations Today blog as the East-Asia and Pacific Editor.
 Cox, W, “How much of the world is covered by cities?”, NewGeography, 2010
 Central Park: The Complete Guide to New York’s Central Park
 Wills, M, “The Real Reason Why NYC’s Skyscrapers Are Where They Are”, JSTOR Daily, 2017
 “Manhattan Population 2018”, World Population Review
  Murphy, D, “Where is the world’s densest city?”, The Guardian, 2017
 Frank, R, “What $1 million buys in real estate around the world”, CNBC, 2018
 “Cities with the most skyscrapers”, Emporis
 “Obstacles & height control”, Civil Aviation Authority of Singapore
 “Fact sheet: geography and population”, Gabinete de Comunicação Social da R.A.E. de Macau
 “Such quantities of sand”, The Economist, 2015
 “Why Hong Kong is about to make a costly mistake in reclamation for East Lantau Metropolis”, South China Morning Post, 2018
 Howarth, D, “New York’s skyscraper are taller and skinnier than ever before”, Dezeen, 2016
 Loh, C, “What land shortage?”, South China Morning Post, 2009
 Ka-Sing, L, “What would entice developers to turn vast farmland holdings in New Territories into nearly 280,000 low-income flats?”, South China Morning Post, 2018