Urban spatial structure

INTRODUCTION

Urban spatial structure or urban structure is the arrangement of urban public space. The way that urban public space is arranged affects many aspects of how cities function and has implications for accessibility, environmental sustainability, safety, social equity, social capital, cultural creativity and economics.

Cities urban structures have been shaped by economic forces, they have been very seldom the result of design.

1.     Large labor market have increasing return to scale.

2.     Large labor markets favor both employers and employees, this is why both move to large cities.

3.     There are a number of  spatial implications if we agree that cities are primarily large labor markets:

a.     Employees and employers are looking competitively for each other and therefore labor mobility is essential

b.     Households, whatever their location, should be able to reach within a reasonable time (say less than 1 hour) all the locations where jobs are offered;

DEFINITION OF URBAN SPATIAL STRUCTURE

The spatial structure of a city can be defined by its:

1. Land consumption

i. Footprint

ii. Average density

2. Spatial distribution of population

i. Density profile

ii. Dispersion index

iii. Eccentricity

3. Pattern of daily trips

i. Monocentric cities

ii. Polycentric cities

City change and growth are inevitable, and development pressures are a given. Nevertheless, a city with foresight and insight can guide and manage public and private development to ensure the best possible outcome for its inhabitants. This best possible outcome includes the protection and enhancement of the city’s key economic, social and environmental resources and assets, and the extension of these economic, social and environmental opportunities to everyone in the city.

The overall intention of the Lafia Town Spatial Development Framework is to guide and manage urban growth, and to balance competing land use demands, by putting in place a long term, logical development path that will shape the spatial form and structure of Lafia town. In the context of climate change and resource depletion, including finite oil resources, the future growth path needs to underline the importance of sustainable future growth.

This proposed development path must be flexible and adaptive, and therefore does not include fixed deadlines and timetables, as economic, environmental and social forces are unpredictable, and it is impossible to determine accurately how fast the city will grow.

The proposals set out below may take decades to realise, and will need to be reviewed from time to time to ensure that they remain relevant, realistic and informed by changing dynamics and local, national and global events.

Purpose of the Spatial Development Framework in Lafia

The spatial development framework  is a long-term (±20-year) plan to manage growth and change in Lafia town. It:

·        provides a long-term vision of the desired spatial form and structure of Lafia Town;

·        Aligns the City’s spatial development goals, strategies and policies with relevant national and provincial spatial principles, strategies and policies;

·        Guides the proposals contained in the more detailed District

Density profiles in Lafia

1.     The profile of densities is key to understanding a city’s structure and its livability.

2.      Cities where the land market works reasonably well have a common structure: densities decrease from the city center outward.

3.     Density profiles are, in most cases, market driven, not design driven, hence the quasi universality of their exponential negatively sloped gradient (see next 3 slides).

Accessibility of the CBD in Lafia

1.     The profile of density shown on previous slides indicates the relative dominance of the city center, if any.

2.     The cumulative number of people residing within a given distance from the CBD explain in quantitative terms the different role of the CBD in various cities.

3.     Higher average density is not equivalent to shorter trips and higher transport efficiency.

4.     The average distance per person to the CBD varies widely between cities with the same areas or the same density.

Pattern of daily trips

1.     The density profiles represent the spatial distribution of the population during the night (midnight density).

2.     During the day the population will move around the city and will create new constantly changing density profiles.

3.   

Knowing the “midnight density” is useful as it is the point of departure of daily trips, however it is the pattern of daily trips which represent the best the way the labor and consumer market work.

Trips pattern in Lafia

1.     The monocentric model is the most common, but it seldom fit entirely the reality on the ground.

2.     The polycentric model “urban village” type is an utopian concept invented by urban planners; it existence would contradict the increasing return to scale of large labor markets.

3.     The polycentric model is increasingly common in Lafia .

4.     In reality no city is purely monocentric or purely polycentric, most cities are a mix of the 2 modes with one mode being the dominating mode.

Linkages between spatial structure and transport in Lafia

1.     In monocentric cities most trips have multiple origins but one “clustered” destination;

2.     In polycentric cities most trips have multiple origins and multiple destinations;

3.     Transit systems can operate efficiently in monocentric cities but are difficult to operate in polycentric cities.

Spatial structure and transport for Lafia

1.     The lower the density, the less frequent the transit service. Where transit service is infrequent potential passengers are forced to use individual means of transportation: car, two or three wheelers. This might be increasingly the case in large cities of Asia and in Central and Eastern Europe.

2.     Empirical evidence suggests that at densities below 30 p/ha transit is neither financially feasible for the supplier nor practical for the consumer.

To summarize:

1.     Cities which are dominantly monocentric have more chance to maintain a high share of transit mode than cities which are dominantly polycentric.

2.      In urban areas where density drop below 30 p/ha the majority of trips are unlikely to be made by transit.

3.     Cities with high densities in dispersed locations may maintain a high share of trips made by transit, but transit is more costly to operate than when high densities are clustered around the CBD.

REFERENCES

Bentley, I. et al. (1985) Responsive Environments: A manual for designers, London: The Architectural Press

Alexander, C.(1996) A City is Not a Tree, in Le Gates, R & Stout, F. (Eds) The City Reader, London: Routledge

Alexander, C.(1983) A Pattern Language