Urban Density refers to the way people and buildings interact.
Urban density is a term used in planning and design to refer to the number of people inhabiting a given urbanized area. As such it is to be distinguished from other measures of population density. Understanding Urban density provides important insights of how cities function. Research related to urban density occurs across diverse areas, including economics, health, innovation, psychology and geography as well as sustainability
In debates about urban density, we often find comments about buildings being too tall or not tall enough, about too many people in a neighbourhood or too few, about streets and buildings being overcrowded or empty.
We are told that Melbourne is building at four times the density of Hong Kong. As these debates over density in Australian cities continue, what is most often missing is any clear understanding of what people mean when they use the word “density”.
Is it the volume or height of buildings? Or is it the numbers of people? One person’s high density may be another’s sprawl; the same tall building may be experienced as oppressive or exhilarating; a “good crowd” for one can be “overcrowded” for another.
We need to clarify whether we are talking about concentrations of people or of buildings. If we take population densities first, these are generally measured as residents per hectare based on census data.
But we also need to distinguish between “internal” and “external” densities – the numbers of people in a room or apartment versus those in an urban precinct. If one look at new high-rise housing in the evening, you can find many apartments unoccupied. At the other extreme, internal crowding largely defines a slum. Building density does not mean population density.
Population densities cannot be based on residents alone since the numbers of people in a given neighbourhood at a given time include those who work there or are visiting. In a mixed-use neighbourhood, residents may be a small proportion of the population density.
There is also the question of streetlife density – of people in public space, of crowds and crowding. Here the complexities multiply. While we can measure the outcomes in pedestrians per minute or per square metre, we are far from understanding the ways in which streetlife is geared to building and population densities.
Building orientation is also an important aspect. How the building interacts with the street. How the inflow and outflow of traffic from a railway station and bus station is also crucial.
Sustainability
It is often asserted that higher density cities are more sustainable than low density cities. Much urban planning theory, particularly in North America, the UK, Australia and New Zealand has been developed premised on raising urban densities, such as New Urbanism, Transit-oriented development, and Smart growth. development, and Smart growth. This view suggest that high density is good for cities as it gives financial viability to city infrastructure.
However, the link between urban density and aspects of sustainability remains a contested area of planning theory. Jan Gehl, prominent Urban Designer and expert on sustainable urbanism, argues that low-density, dispersed cities are unsustainable as they are automobile dependent. A minority, such as Randy O’Toole of the Libertarian Cato Institute, counter that raising densities results in more expensive real estate, greater road congestion and more localized air pollution. Others counter that traffic congestion is a result not of population density but of parking capacity.[ At a broader level, there is evidence to indicate a strong negative correlation between the total energy consumption of a city and its overall urban density, i.e. the lower the density, the more energy consumed.
Measurement
Urban density is a very specific measurement of the population of an urbanized area, excluding non-urban land-uses. Non-urban uses include regional open space, agriculture and water-bodies.
There are a variety of other ways of measuring the density of urban areas:
- Floor area ratio – the total floor area of buildings divided by land area of the lot upon which the buildings are built
- Residential density – the number of dwelling units in any given area
- Population density – the number of human persons in any given area
- Employment density – the number of jobs in any given area
- Gross density – any density figure for a given area of land that includes uses not necessarily directly relevant to the figure (usually roads and other transport infrastructure)
- Net density – a density figure for a given area of land that excludes land not directly related to the figure.
- Weighted density – a density metric which measures the density at which the average citizen lives. It is determined by calculating the standard density of each census tract, assigning each a weight equal to its share of the total population, and then adding the segments.
A small interesting video about urban density
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