1. Brief background
According to Abraham Maslow’s human needs, a man’s basic needs are foods, clothing and shelter. One of the Sustainable Development Goals (SDG) of the United Nations is Sustainable Cities and Community (Goal 13). Rapid and continuous growth of our urban centres by rising population or increase in migrations is a major concern. According to United Nation, in 2018, there are 4.2 billion people living in the world, 55 percent of the world’s population, lived in cities. By 2050, the urban population will reach 6.5 billion. Developing countries will experience increase in population in the coming years (UNDP, 2018). To build sustainable communities, our urban space must be managed properly to provide career and business opportunities, safe and affordable housing, and building resilient societies. There is a nexus between Population and housing, population growth means increase in housing demand. Housing affects the productivity of the citizen that in return affect a nation’s GDP.
Slums are becoming a more significant feature of our urban life about 828 million people are living in slum areas in the world (UNDP, 2018). Slum areas are areas with non-standard and poor quality housing units with are often associated with lack of standard conveniences such as electricity and water supply UNIHABITAT 2007). The proportion of urban population living in slums in 2012 was highest in Sub-Saharan Africa (62%), followed by Southern Asia (35%), Southeastern Asia (31%), Eastern Asia (28%), Western Asia (25%), Oceania (24%), Latin America and the Caribbean (24%), and North Africa (13%). (UNIHABIT, 2012). Urban Slums are form and grow for many different reasons such as unchecked population growth, rapid urban migration, non-performing economics, high unemployment, poverty, poor city planning, politics, natural disasters and social conflicts.
The population of Nigeria stands at 197,430,516 people as at October 2018. The population is about 2.57% of the world population. About 55%-60% of the population live in urban areas; the population density is 215/km2 of the total area of 923,768km2. According to the World Bank estimates, Nigeria still has housing deficit of about 17 million units that will require over 390 USD Billion to fix. The capital value and rental value of housing is relative high in Nigeria compare to the people’s income; there are two dearth outcomes of the current housing situation, there are high quality house which is inadequate that are unaffordable and there are low quality which is adequate but inaccessible. Many of Nigeria’s citizens spent large part of their annual income to pay rent-associated fees.
The poor performance of the economy encourages slum development. Nigeria’s increasing population do not match the economic growth, thereby reduces per capital disposal income. Despite the improvement in economic term, there is little reflection on the standard of living of the people. However, with little economic incentive available, it is more likely to develop middle-income housing rather than low-cost housing for the growing population. Few housing units are built for many low-income earners in the country. In the face of the economic realities, people continue to migrate from rural area to urban areas to stay in slums in search for better livelihood. Most opportunities for employment available in the urban centres make no provision for housing.
Multiple agencies responsible for generating urban policies have not been able to effect urban improvements. Rather, duplication of functions and lack of coordination has affected the entire city development. There are cases of conflicts of jurisdiction and competence, the absence of effective coordination between levels of government, frequent bureaucratic changes, low priority for urban planning, and the commensurate lack of funding have caused delays and confusion in the execution of urban policies. This encourages the expansion of slums
The ongoing herdsmen-farmer conflict in the country, and the Bokoharam insurgence in the northeast of Nigeria, has given rise to a many of refugees and Internal Displace Persons (IDP) camps. Many of these camps are located in slums area around the urban cities. Some of the largest slums of the world are in areas of political or social conflicts. (Mike Davis, 2006).
This is the background to the study of how we can through conscious policies and political will to build a sustainable city and ensure that we address the issue of the growing slums in our urban centres. Some solutions are suggested and recommendations are made.

2. Identified Problems backed with evidences
Violence
There is a popular saying ‘slums breed crime’, UN-Habitat reports that some slums are more exposed to crimes with higher crime rates. Most slum areas are brewing ground for illicit arm deals and consumption of hard drugs. It is estimated that crime rates are higher in some slums area than the city. The organised crime networks find their hiding place in slums areas, although not everyone living in the slums are criminals but it serve as a safe haven for criminal activities. Violence can have strong, negative impacts on economic development by drastically reducing growth and producing long-lasting detrimental social impacts (World Bank, 2009). At the national level, the costs of violence can add up to a substantial portion of the GDP and harm economic growth. There are various degrees of violence prevalent in slum area raging from physical to sexual violence; there are reported cases of women sexual harassment to rape of young women.
Cohen as well as Merton theorized that the cycle of slum violence does not mean slums are inevitably criminogenic, rather in some cases it is frustration against life in slum, and a consequence of denial of opportunity to slum residents to leave the slum.( Cohen and Merton, 1971)
Slums are often non-secured areas, women and children often live in danger they are the most vulnerable in times of violence. Conflict and violence management is not effective in slum areas because of the planning and condition of the area, the location and layout of the areas sometimes make is difficult for quick response from the police, and other law enforcement agencies usually find it very difficult to carry out their operations, there is also poor intelligence gathering in slum areas.
The continuous growth of slums will continue to threat the security of the our cities and the nation at large if not put in check

Flooding
Slum areas have over-concentration of people in a relatively small space that is highly susceptible to floods. Sometimes slums settlements are located on flood prone terrain, and there are no flood controls in place to check flood. Flood is a recipe for outbreaks of waterborne diseases, which is very dangerous to the public health. Flooding decreases the access to clean drinking water, which has adverse effect on the development of the city.
Floods have led to tremendous losses of property, infrastructure, business and increased risk of diseases. For example, the Ogunpa flood, which occurred in Ibadan in 2011, resulted in a tremendous number of casualties. It was documented that about 25% of households in Ibadan lost their livelihoods, as their businesses were adversely affected (WHO 2012). Ogunpa as also identified as one of the slum areas of Ibadan. Similar to this case were floods in the states along the rivers Niger and Benue in 2012 and 2017, Lagos in 2011, 2012 and 2017 as well as the Niger Delta regions in 2012.
According to Adegoke (1989) waste collection in Nigeria is irregular and restricted to major cities. For the slum communities there is the absence or lack of proper refuse dumps and sewerage system. Therefore, wastes are disposed indiscriminately around; the wastes block the water ways and flood channels. Flooding in urban settlements is compounded by inadequacy of the drainage network within the city, urban areas in Nigeria drainage system are not functioning properly. Unfortunately, slums areas with poor people suffer more from the consequences of floods.

Public Health
Slum areas have high reported cases of disease outbreak due to the poor planning and declining access to health facilities. Slums have been historically linked to epidemics, and disease outbreak. For example, the slums of West African nations such as Liberia were crippled by as well as contributed to the outbreak and spread of Ebola in 2014(Wikipedia 2014). Slums are considered a major public health concern and potential breeding grounds of drug resistant diseases for the entire city, the nation, as well as the global community. The practise of open defecation on the land or stagnant water bodies such as rivers and streams is prevalent in slum areas; because most areas do not have access to good toilet and public toilet are often not available. The available sources of water are rivers and streams that are often polluted due to the activities of the dwellers. Poor water quality is the cause of many major illnesses including malaria, diarrhoea and trachoma (WHO, 2004). There is a higher rate of disease transmission of disease in slums with high population densities; the spread of communicable diseases is very ease (cholera and diarrhoea, tuberculosis) because of the frequent contact. Because of the lack of health facilities and services in these areas, there are low vaccination rates; little children do not have access to vaccination against some diseases in their early childhood. The children are more vulnerable to disease spread in these areas. Moreover, health service is insufficient or inadequate in slum areas, emergency ambulance service and urgent care services are typically unavailable, as health service providers avoid to serve in slum areas. Throughout slum areas in various parts of the world, infectious diseases are a significant contributor to high mortality rates.
Children in slum areas suffer malnutrition; child malnutrition is more common in slums than in non-slum areas. The cases of child malnutrition in slums are caused by poverty, poverty may cause the parents not to be able to provide food for the children because they cannot afford to buy and store enough food, which often leads to malnutrition.

Building collapse
Slums areas have more poor constructed building that are occupied by large number of people. The population density of these areas put a significant pressure on few building in the area. There are some reported cases of building collapse in Nigeria from independence. Folagbade (2001) stated that about forty-two (42) cases of building collapse as occurring between 1980 and 1999 in Nigeria while Makinde (2007) listed fifty-four (54) cases occurring between January 2000 and June 2007 alone. Building collapse has been observed to cut across the different categories of building – private, corporate or public. The federal ministry of Power, Works and Housing stated that from 2011 to 2016, a total of 54 building collapsed across the country within a period of four years (Punch. 2018)
Although there is no clear study that says that much of the collapse occur in slums areas, but some of the factors attributed to the collapse of these building are prevalence in the urban slum areas, which include building without approval, poor construction materials, poor technical supervision on work, weak foundation, structural defection and lack of maintenance. These factors are responsible for the growing building collapse in the country.
On the other hand, many lives and properties have been loss due to the incident of building collapse in Nigeria. The Standard Organisation of Nigeria (SON, 2017) has reported that 3235 people have died, 252 building collapsed, and resources worth 3.5 billion naira lost from 2007 to 2018 in the country (Sahara Reporters, 2018). For our cities to be sustainable, we have to tackle the issue of building collapse in Nigeria.

4. Policy Options
Urban planning with infrastructural development
Government should take a deliberate measure in building urban centres. Adequate planning of urban space will discourage the growth of slums. Massive investment in infrastructural will speed up economic growth and provide employment opportunities for the citizens. Infrastructural investment in housing will provide more affordable house to low-income earner and it will reduce rent for available housing units in Nigeria.
Urban centres and its metropolis should be adequate plan to accommodate future expansion and development, the increasing population should be put in to consideration in city planning. Urban spaces planning and development should be taken regularly to avoid the re-emergence of slums areas in our urban centres. There are various agencies of the government saddled with the responsibility of city planning and developments; there should be proper enforcement of the laws and regulations in the cities, to prevent slum growth.
Adequate budget allocation should be given to urban infrastructural development; this will empower various government agencies to perform their duties. Maintenance of urban centre facilities is capital intensive; the government can collaborate with private investor in the housing sector to provide basic infrastructural facilities in Nigeria.

Standard Regulation in the housing Sector
One of the problems of the housing sectors is the weak implementation of policies and poor execution of planned programmes. The ineffective of government enforce of standard and quality in the planning, design and design of building and other infrastructural facilities have given rise to slums.
There must be due process followed from the award of various contractors and company implementing some project, the contractors must follow the set down standards to deliver a good quality product.
There is a creation of a national policy that we guild the ownership and rentages of houses in Nigeria. From survey, many houses are available for rent but the cost of rent is relatively high in urban area. If there is a policy that can ease the access to land, monitoring of the standard .To provide good housing that is affordable to the low income earners, government must be involve in providing more public housing scheme to the people
Slum upgraded task force
The government can organised a task force that will oversee the relocation of some slums in urban areas to other places that will not post any threat to the city development. The slum residents should be made aware and convinced that their current location is a health hazard, prone to natural disaster, and provided with a better option of relocation to an alternative location that is well connected to opportunities in he city. Some slums residents may be difficult to relocate because of social or cultural factor, such slums areas can be provided with basic infrastructural facilities such as safe drinking water, electricity distribution, good drainage systems and transportation system. The approach will be that, the slum areas will not be destroyed and slum residents will not be evicted, the residents will be engaged to rebuild their own society to become a better community to live, which can over time attract investment from government organizations and businesses.
While the legislative arm of the government is required to provide a strong legislative law for the success of the project and provide oversight function for the continuation of the project. There will be an initial evaluations of the work, as part of the, evaluations will also done 5 to 10 years after a project started to determine the extent of the impact of the project.
Mortgaging financing
Housing schemes are very capital intensive, the government can provide financing for housing projects by mortgaging financing. Mortgage financing remains a very small percentage of Nigeria’s GDP, at 0.5 percent. In comparison to Ghana (2 percent), South Africa (31 percent), US (77 percent) and UK (80 percent) (Global Findex, 2014).
On the other hand, fund liquidity for commercial banks should also be checked, the commercial banks should be able to provide long term loan of 25 years and above for prospect developer and investors for a good housing units for low-income earners. The loan must be secured and back by the federal government by the central bank of Nigeria, in case of shortage of funds.
The operation of the national mortgage refinance corporation set up in 2013 should be checked to ensure that there are projects embarked upon to produce the necessary housing units to the populations in Nigeria. The activities of this corporation should be promoted and bring to the public. The ministry of works and housing should come with policies that will ease access to loans to low-income earner in the society.

Conclusion
In conclusion, it is important to note that there is a connection between population and housing; increase in population means more housing have to be provided. Our cities are experiencing population explosion by either migration or urbanization. There must be adequate measures to cope with the ever-increasing pressure on the urban centres facilities. Although there are existing government, strategies, programmes and project to address the housing challenges in Nigeria. The government should be conscious in the planning and development of city to the accommodate the current population and adequate for further development. There must also be deliberate actions in the implementation of regulations and laws that will regulate the housing sector in Nigeria.
There are two dearth outcomes of the current housing situation in Nigeria, there are high quality and inadequate house that are unaffordable and there are low quality and adequate houses that are inaccessible. The housing units available are mostly for the middle-class, fewer housing units are available for the low-income earners in the country.
The upgrading and development of slum areas are is a particular interest to this study, because of the growth and expansion of slums in our urban spaces, adequate monitoring actions should be taken to check the expansion of slums. The government can collaborate with civil societies, Non-Governmental Organisations and international organisation like Slum Dwellers International (SDI), World Health Organisation and United Nations (UN) on the development of slum areas.

5. Recommendations
Based on the review of the existing work and the research finding in this study. The following are hereby recommended.
1. Government should invest in the infrastructural development of the country. This way, the socio- economic condition of the citizens will improve. Poverty level will also reduce, so that the urban dwellers will be able to afford a rent or own a house.
2. Government at all level should constitutes a task force that will be backed by law to monitor the situation of slums in the country. The taskforce should work be able to identify slum areas in the city and the reasons responsible for the slum area, adequate measures should be implemented to prevent the growth and expansion of slum areas.
3. Interested investor and individuals that wish to invest in property and housing sector should be given access to credit facilities in terms of long-term loan and mortgage financing. Government should form partnership with private investors to provide massive housing units for low-income earners.
4. There should be effective implementation of government policies on housing. Appropriate regulations concerning the land use, land title and acquisition of property should be vigorously pursed in the urban centres.

References
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Folagbade, S.O. (2001): Case Studies of Building Collapse in Nigeria. Proceedings of a Workshop on Building Collapse: Causes, Prevention and Remedies. The Nigerian Institute of Building, Ondo State Chapter, 23-24 October
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UNIHABITAT (2007) What are slums and why do they exist? Archived 2011-02-06 at the Wayback Machine UN-Habitat, Kenya (April 2007)
UNIHABITAT 2012 State of the World’s Cities Report 2012/2013: Prosperity of Cities” (PDF). UNHABITAT. Retrieved on 4 June 2019
Wikipedia 2014. In a Liberian slum swarming with Ebola, a race against time to save two little girls. The Washington Post
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