Understanding Density And High Density - WordPress
1Understanding Density and High DensityVicky ChengThe word ‘density’, although familiar at first glance, is a complex concept upon closer examination.The complexity mainly stems from the multitude of definitions of the term in different disciplines andunder different contexts. This chapter attempts to untangle the intricate concepts of density accordingto two perspectives – namely, physical density and perceived density. A thorough comprehension ofthese two distinct concepts of density will serve as a basis for understanding the meaning of highdensity. Hopefully, this chapter will establish the ground for the discussions in later chapters on thedesign of high-density cities with respect to the timeliest social and environmental issues.Physical densityPhysical density is a numerical measure of theconcentration of individuals or physical structureswithin a given geographical unit. It is an objective,quantitative and neutral spatial indicator. However, inpractice, physical density takes on a real meaning onlyif it is related to a specified scale of reference.For instance, density expressed as ratio ofpopulation to land area can vary significantly withreference to different scales of geographical unit. TakeHong Kong as an example: if the land area of the wholeterritory is taken into account, the overall populationdensity in Hong Kong is about 6300 persons per squarekilometre. However, only about 24 per cent of the totalarea in Hong Kong is built up. Therefore, if thegeographical reference is confined to built-up land,then the population density will be about 25,900individuals per square kilometre, which is four timesthe overall density of the territory. Hence, it isimportant that the scales of geographical references beexplicitly defined in density calculation, otherwisecomparison of density measures will be difficult.Nevertheless, there is no standard measure of density;there are only measures that are more widely used thanSource: Vicky ChengFigure 1.1 People densityothers. In town planning, measurement of physicaldensity can be broadly divided into two categories: peopledensity and building density. People density is expressed
4 AN UNDERSTANDING OF HIGH DENSITYSource: Illustration redrawn by Vicky Cheng, adapted from GreaterLondon Authority (2003, p11)Figure 1.3 Net residential areaSource: Vicky ChengFigure 1.2 Building densityas the number of people or household per given area,while building density is defined as the ratio of buildingstructures to an area unit. Common measures of peopleand building densities are outlined as follows.Measures of people densityRegional densityRegional density is the ratio of a population to the landarea of a region. The reference area is usually defined bya municipal boundary and includes both developedand undeveloped land. Regional density is often used asan indicator of population distribution in nationalplanning policy.Residential densityResidential density is the ratio of a population toresidential land area. This measure can be furtherclassified in terms of net and gross residential densitiesbased on the definition of the reference area. However,there is no consensus on the definition of net and grossareas; it varies across cities and countries. In the UK,net residential area refers only to land covered byresidential development, along with gardens and otherspaces that are physically included in it; this usually alsotakes into account half the width of adjacent roads(TCPA, 2003). In Hong Kong and some states in theUS, net residential area only consists of the parcelsallocated for residence where internal road, parks andother public lands are excluded (Churchman, 1999;Hong Kong Planning Department, 2003).Source: Illustration redrawn by Vicky Cheng, adapted from GreaterLondon Authority (2003, p11)Figure 1.4 Gross residential areaThe measure of gross residential density considers theresidential area in its integrity. In addition to the areaallocated for residence, it also takes into account nonresidential spaces such as internal roads, parks, schools,community centres and so on which are meant to servethe local community. Nevertheless, in practice, it isdifficult to clearly define the extent of theseresidentially related areas. Some developments maytake into account lands for purposes of serving a widerneighbourhood and others may include nondevelopable land such as steep slopes. Thisinconsistency of inclusion leads to great ambiguity ingross density measurement and, in turn, makescomparison difficult.Occupancy densityOccupancy density refers to the ratio of the number ofoccupants to the floor area of an individual habitableunit. The reference habitable unit can be any kind ofprivate or public space, such as a dwelling, office,theatre and so on. However, the reference area usually
UNDERSTANDING DENSITY AND HIGH DENSITY 5refers only to an enclosed area. Occupancy density is animportant measure in building services design as itprovides an indicator for estimating the servicesrequired. For instance, the electricity demand, spacecooling and heating load, provision of fire safetyfacilities, and so forth are estimated based on theoccupancy density.Occupancy rate, which is the inverse measure ofoccupancy density (i.e. ratio of floor area of individualunit to number of occupants), is commonly used as anindicator of space available for individual occupants.Higher occupancy rate means larger habitable area forindividual occupants. Regulation of minimumoccupancy rate is often used in building design tosafeguard the health and sanitary condition of habitablespaces.resources required for construction; consequently, itcan forecast the financial balance of investment andreturns.Measures of building densityPlot ratio (floor area ratio)Plot ratio is the ratio of total gross floor area of adevelopment to its site area. The gross floor areausually takes into account the entire area within theperimeter of the exterior walls of the building, whichincludes the thickness of internal and external walls,stairs, service ducts, lift shafts, all circulation spaces,and so on.Site area refers to the total lot area of thedevelopment, which, in most cases, is precisely definedin the planning document. Since the definitions ofboth floor and site areas are relatively clear in themeasurement, plot ratio is considered as one of themost unambiguous density measures.In planning practice, plot ratio is extensivelyadopted as a standard indicator for the regulation ofland-use zoning and development control. Differentplot ratios for different types of land uses are oftenspecified in urban master plans as a provision ofmixed land use. Furthermore, maximum plot ratio isoften controlled in the master plan in order togovern the extent of build-up and to prevent overdevelopment.In building design, plot ratio is widely used indesign briefing and development budgeting as itreflects the amount of floor area to be built and,hence, can be used to estimate the quantity ofSource: Vicky ChengFigure 1.5 Plot ratio 1Source: Vicky ChengFigure 1.6 Plot ratio 1.5
6 AN UNDERSTANDING OF HIGH DENSITYSource: Vicky ChengFigure 1.9 Site coverage 50 per centSource: Vicky ChengFigure 1.7 Plot ratio 2Site coverageSite coverage represents the ratio of the buildingfootprint area to its site area. Therefore, site coverage isa measure of the proportion of the site area covered bythe building. Similar to plot ratio, site coverage ofindividual developments is often controlled in urbanmaster planning in order to prevent over-build and topreserve areas for greenery and landscaping.The open space ratio, which is the inverse measureof site coverage, indicates the amount of open spaceavailable on the development site. However, the term isSource: Vicky ChengFigure 1.8 Site coverage 25 per centsometimes also expressed as area of open space perperson and this measure is used by the planningauthority to safeguard a reasonable provision ofoutdoor space for the population.Apart from plot ratio and site coverage, otherdensity measures, such as regional and residentialdensities, can also be expressed in terms of buildingdensity. Measurement of residential density with respectto number of dwellings per land area is an importantindicator in the making of planning policy. In the UK,for instance, the government has set a residential densityof 30 dwellings per hectare as the national indicativeminimum for new housing development (UK Office ofthe Deputy Prime Minister, 2006).Density gradient and density profileThe density measures discussed so far are based onaverages over a land area. These measures can properlyreflect reality if people or buildings are fairly evenlydistributed over the entire area. However, in manycases, especially when the reference geographical unit islarge in scale, the distribution pattern of people orbuildings can vary significantly.Take Hong Kong as an example: the averagepopulation density over the entire territory is about6300 persons per square kilometre. Nevertheless, thedistribution of the population is very uneven acrossdistricts, ranging from 780 people per square kilometrein the outlying islands to 52,000 people per squarekilometre in the urban area (Hong Kong Census andStatistics Department, 2006).
UNDERSTANDING DENSITY AND HIGH DENSITY 7Source: Vicky ChengFigure 1.10 Hong Kong population density map(magnitude represented in height): high density in thecentral urban area and low density in outlying islandsIn order to address the spatial variation of density, othermeans of density measurements, such as densitygradient and density profiles, have been introduced.Density gradientDensity gradient is defined as the rate at which densityfalls (according to distance) from the location ofreference; therefore, a positive density gradient denotesa decline of density away from the reference location.The density gradient is usually derived from densitiesmeasured in a series of concentric rings at a 10m or20m width, radiating out from the location of thereference (Longley and Mesev, 2002).Density gradient is a composite measure of density.Comparing the changing pattern of density gradientsover time can review the process of spatial evolution.Figure 1.12 shows two changing patterns of densitygradient. Figure 1.12 (a) represents a process ofprogressive decentralization with decreasing populationdensity in the urban centre and increasing density andboarders towards the outskirts. In contrast, Figure 1.12(b) depicts a process of centralization with growingpopulation density in both the urban centre and outskirtsand, at the same time, enlarging borders towards theperiphery. Between 1800 and 1945, the North Americanmetropolis exhibited the former process ofdecentralization, while European counterparts resembledthe latter process of centralization (Muller, 2004).Density profileDensity profile refers to a series of densitymeasurements based on a reference location butcalculated in different spatial scales. Similar to densitygradient, it is a measure of the rate at which density7000Number of people/sq.km60005000400010 20 30 40 m300020001000001234567Distance from reference location/km89Source: Illustration redrawn by Vicky Cheng and adapted from Longley and Mesev (2002, p20)Figure 1.11 Population density gradient from the town centre towards rural outskirts
8 AN UNDERSTANDING OF HIGH DENSITY(a)(b)Population Density Gradient: CentralizationPopulation densityPopulation densityPopulation Density Gradient: DecentralizationPeriod:Stage 1Stage 2Stage 3Period:Distance from town centreStage 1 Stage 2 Stage 3Distance from town centreSource: Illustration redrawn by Vicky Cheng and adapted from Muller (2004, p62)Figure 1.12 Density gradients over time: progress from stage 1 to stage 3 – (a) progressive decentralization withdecreasing population density in the urban centre and increasing density towards the outskirts; (b) centralization withgrowing population density in the urban centre and outskirts, as well as enlarging borders towards the peripherychanges away from the reference location and is used asan indicator of settlement structure.Density profile has been adopted in the UK as thebasis for rural definition. In the UK rural classificationsystem, density profile is calculated based on land areaenclosed by a series of concentric circles of 200m,400m, 800m and 1600m radii. The variation of densityat these successive scales is then used to characterize thespatial structure of different settlements. For example, avillage as defined in the classification system has thefollowing properties: a density of greater than 0.18 residences perhectare at the 800m scale;a density at least double of that at the 400m scale;anda density at the 200m scale at least 1.5 times thedensity at the 400m scale (Bibby and Shepherd,2004).Through comparing the measured density profile withthe predefined profiles, settlements of different spatialstructures can be classified.Household densityUnit hectare024 816 100mSource: Vicky ChengFigure 1.13 Density profile calculated overconcentric circles of radii of 200m, 400m,800m and 1600m
UNDERSTANDING DENSITY AND HIGH DENSITY 9Building density andurban morphologyBuilding density has an intricate relationship with urbanmorphology; it plays an important role in the shaping ofurban form. For instance, different combinations of plotratio and site coverage will manifest into a variety ofdifferent built forms. As illustrated in Figure 1.14, thebuilding transforms from a single-storey building to amulti-storey tower as the proportion of site coveragedecreases.In a similar vein, urban developments of the samedensity can exhibit very different urban forms.Figure 1.15 shows three settlements with the sameresidential density of 76 dwellings per hectare, but indifferent urban forms: multi-storey towers, medium-risebuildings in central courtyard form, and parallel rows ofsingle-storey houses. Intrinsically, the three layouts aredifferent in many aspects; nevertheless, in terms ofurban land use, the proportion and organization ofground open space is of particular interest.The high-rise layout creates large areas of open landthat are suitable for expansive communal facilities, suchas libraries, sports grounds and community centres.Nevertheless, without efficient land-use planning, thesespaces can run the risk of being left over, not properlymanaged and end up producing problems.The proportion of open area resulted in themedium-rise courtyard form, although it is less thanthat of the high-rise layout. However, unlike theformer, the courtyard space is enclosed and clearlydefined. It can be shaped as the central stage of thecommunity and, thus, encourages full use of space.Plot ratio 1, Site coverage 100 per centThe single-storey houses layout, on the other hand,divides open space into tiny parcels for individual uses.In this arrangement, the area for communal facilities islimited; nevertheless, residents can enjoy their ownprivate open space.In the face of rapid urbanization, the relationshipbetween building density and urban form has attractedwide interest. Growing pressure of land scarcity as aconsequence of increasing urban population hasinitiated extensive investigation on the spatial benefit ofmulti-storey buildings. Mathematical and geometricalanalyses have been conducted to address the issue,particularly concerning the relationships betweenbuilding height, plot ratio, site coverage and solarobstruction (Gropius, 1935; Beckett, 1942; Segal,1964; Martin and March, 1972; Evans, 1973;Davidovich, 1968).For an array of continuous courtyard form at agiven plot ratio, increased building height will alwayslead to reduced solar obstruction, as shown in Figure1.17. Or, to put it another way, provided that thesolar obstruction angle is kept unchanged, increasedbuilding height will heighten the plot ratio.Moreover, the site coverage will decreaseconcurrently, which will lead to more ground openspace.For urban form with an infinite array of paralleltenement blocks, although geometrically different fromthe courtyard form, the mathematical relationshipsbetween building height, plot ratio, site coverage andsolar obstruction remain the same. Therefore, theobservations obtained from the courtyard form applyto the parallel block form as well.Plot ratio 1, Site coverage 25 per centSource: Vicky ChengFigure 1.14 Two built forms with the same plot ratio but different proportions of site coverage
10 AN UNDERSTANDING OF HIGH Source: Illustration redrawn by Vicky Cheng and adapted from Rogers(1999, p62)Figure 1.15 Same density in different layouts: (a) multistorey towers; (b) medium-rise buildings in centralcourtyard form; (c) parallel rows of single-storey housesFor urban form with an infinite array of towers at a lowsolar obstruction angle (below approximately 45 ),increased building height will always lead to a reducedplot ratio. At high solar obstruction angles (aboveapproximately 55 ), increased building height mayincrease the plot ratio initially, but further incrementwill result in a reduced plot ratio.(c)Source: Illustration redrawn by Vicky Cheng and adapted from Martinand March (1972, p36)Figure 1.16 Three different urban forms: (a) courtyard;(b) parallel block; (c) towerNevertheless, increased building height will decrease thesite coverage in both cases. Finally, compared to thecourtyard and the parallel block forms, at a given solarobstruction angle and building height, the tower formwill always lead to a lower plot ratio and lower sitecoverage.In reality, site area is usually limited and urban formis very often determined by the predefined developmentdensity. Figure 1.18 shows the residential densities of
UNDERSTANDING DENSITY AND HIGH DENSITY 11Source: Vicky ChengFigure 1.17 Relationships between building height, plot ratio, site coverage and solar obstructionSingle family houses25–40 units/net hectareMulti-storey townhouses50–100 units/net hectareHigh-rise apartment blocksMulti-storey apartment blocks1000 units/net hectare120–250 units/net hectareSource: Vicky ChengFigure 1.18 Residential densities of four different urban forms
12 AN UNDERSTANDING OF HIGH DENSITYseveral existing urban forms (Alexander, 1993; Ellis,2004; Campoli and MacLean, 2007).Perceived densityPerceived density is defined as an individual’sperception and estimate of the number of peoplepresent in a given area, the space available and itsorganization (Rapoport, 1975). Spatial characteristicper se is important in the perception of density; but inaddition, the interaction between the individual andthe environment as a whole counts even more.Individual cognitive attributes and socio-culturalnorms are also factors that contribute to thisinteraction (Alexander, 1993).Furthermore, perceived density not only addressesthe relative relationships between individual and space,but also between individuals in the space. For example,suppose there are two spaces with the same occupancyrate of 3 square metres per person; in one case, there isa group of friends in a clubroom, while in another thereare several unacquainted people in a small lobby.Clearly, these two situations are very different in socialand perceptual terms, even though they show the samephysical density (Chan, 1999). In order to distinguishbetween these two different aspects of perceiveddensity, the concept of spatial density and social densitywere introduced.Spatial density refers to the perception of densitywith respect to the relationship among spatial elementssuch as height, spacing and juxtaposition. High spatialdensity is related to environmental qualities, such ashigh degree of enclosure, intricacy of spaces and highactivity levels, in which all of these qualities tend toresult in higher rates of information from theenvironment itself.Social density describes the interaction betweenpeople. It involves the various sensory modalities, theme
these two distinct concepts of density will serve as a basis for understanding the meaning of high density. Hopefully, this chapter will establish the ground for the discussions in later chapters on the design of high-density cities with respect to the timeliest social and environmental issues. Source: Vicky Cheng Figure 1.1 People density
density functional (KEDF) to accurately and efficiently simulate various covalently bonded molecules and materials within orbital-free (OF) density functional theory (DFT). By using a local, density-dependent scale function, the total density is decomposed into a hi
The sphere on the right has twice the mass and twice the radius of the sphere on the left. Compared to the sphere on the left, the larger sphere on the right has A. twice the density. B. the same density. C. 1/2 the density. D. 1/4 the density. E. 1/8 the density. mass m radius R mass
Density of soil is defined as the mass the soil per unit volume. 3. Bulk Density: Define (U) Bulk density is the total mass M of the soil per unit of its total volume. 4. Dry Density: Define (U d) The dry density is mass of soils per unit of total volume of the soil mass. 5. Define: Saturated Density (U sat) When the soil mass is saturated, is .
The Impact of High Population Density on the Built Environment and the Behavior of Individuals in Amman . Elaf Dawodieh . University of Jordan. Abstract- When thinking of high density, one of the most important issues is how we perceive it and how it affects us, the users of high density environments. The built environment affects
Design Guide for High-density Interconnect Structures and Microvias IPC-2226: Sectional Design Standard for High-density Interconnect (HDI) Printed Boards IPC/JPCA-4104: Qualification and Performance Specification for Dielectric Materials for High-density Interconnect Structures (HDI) IPC-6016:
7/7/2015 12 Tissue Heterogeneities – Low density tissues – High density tissues (i.e. Bone) . Iron Composite – Density MVCT – 1.68 0.09 g cm-3 – Density kVCT – 2.67 0.17 g cm-3 – Density Measured – 1.71 0.03 g cm-3 3D Printed Phantoms. 7/7/2015 13 Heterogene
Contents Density predictions using Vp and Vs sonic logs CREWES Research Report — Volume 10 (1998) 10-5 Figure 4. Density (g/cm3) versus Vp (ft/s) for 09-17 well showing the best-fit line through the data. The Vp log is on the right and density on the left. Figure 5. Density (g/cm3) versus Vs (ft/s) f
Albert Woodfox were properly convicted for the 1972 murder of prison guard Brent Miller. Supporters of Wallace and Woodfox, who make up two-thirds of a group known to supporters as the "Angola Three," say that the convictions were at least partly because of the men's involvement with the Black Panther Party. "Under this new governor's office, this new day, we are making sure we right the .
