Chapter 3 METHODS. The primary goal of this section is to explore different methods in which populations of

Transcription

1 Chapter 3 METHODS 3.0 Data 3.1 Overview and Goals The primary goal of this section is to explore different methods in which populations of urban spaces can be visualized in new ways at various scales. The historical growth of Chicago has created a landscape in which a system of boundaries exists that is commonly used in cartographic representations of the city. This boundary system limits the understanding into the complexity of the urban space and the micro-processes of human settlement in Chicago. Traditional choropleth and dot density techniques rely on the established boundary units and represent Chicago s population in a simplified and typically uninformative way. With experimentation in the methodological approach to the problem of urban population distribution, maps and visualizations can be made to better characterize the phenomenon of people in space. The following methods are investigated in the remainder of this chapter to construct different visualizations from the available data: 1. Section 3.2 will explore the vertical residential environment of Chicago and create a new measurement to describe the living spaces of Chicago- the measurement of personal space. 2. Section 3.3 will look at the rationale for and the methodological of comparing demographic profiles as a measure to better understand the significance of the personal space measurement.

2 3. Section 3.4 will consider different exploratory spatial statistic models to describe the geographic distribution of different classifications of living space across the city of Chicago. 4. Section 3.5 will construct a method to visualize the individual person in the landscape of the urban environment. 5. Section 3.6 will investigate an alternative approach to visualize the intensity of people and spaces without the use of traditional boundary units. 3.2 Personal Space Model Vertical Space Problem The origin for the following methods is derived from the second research question of this thesis- in what ways does the vertical extent of neighborhoods obscure our understanding of spaciousness and crowdedness for urban residents. Chicago is considered the to be the birthplace of the skyscraper and boast the tallest building in the United States, the Willis Tower- a 110 story, 1454 foot structure in the Loop (Fountain, 2001). The history of skyscrapers in the redevelopment of post fire Chicago began in 1885 with the completion of the Home Insurance Building, the first steel-framed skyscraper in the world. Originally constructed with a height of 138 feet, the building was later expanded to a height of 180 feet before being demolished in Historically, Chicago has played a prominent role in the development of the skyscraper and at various times in the history of skyscraper development has boasted the world s tallest building (Daniel & Grant, 2005). Louis Sullivan, an urban designer and architect in Chicago recognized that the skyscraper would represent a new form of architecture in the post fire landscape of Chicago (Kaufman,

3 1969). Sullivan discarded conventions and designed buildings that emphasized their vertical nature before adequate technology existed to construct the design. Materials and technologies were invented in order to realize the Sullivan vision for the new urban space. This new form of architecture, with an emphasis on the vertical space, became known as the Chicago School of Design (Kaufman, 1969). Through the 20 th century, Chicago went through two distinct phases of highrise construction- a first boom, from the early 1920s to the mid-1930s, and a second boom from the early 1960s until the present. The spatial distribution of the high rise buildings are mostly concentrated in the Loop and along the Magnificent Mile in Chicago's Near North Side community area (Kaufman, 1969). There are 2,265 high-rises (over 150 feet) structures in the city of Chicago and 903, about 40%, are zoned for residential use. With the amount of vertical residential space in Chicago available, the traditional representations of spaciousness and crowdedness within the boundary units of community area or census block as characterized by population density are inadequate measurements. The measurement of population density will not account for the vertical structure of modern urban residential patterns and could confuse places of high density and places of crowded living conditions. The aim of this method is to create a new measurement which can account for the vertical spaces within buildings and reconstruct the idea of population density into one of personal space.

4

5

6 3.2.2 Model of Vertical Space The first step in the personal space model is a binary dasymetric approach is used to separate residential and non-residential structures throughout the city. This method will take the building footprints for every building in Chicago and eliminates the non-residential structures based on urban zoning codes attached to each building. The binary approach in this context deems single-family and multi-family residential structures as suitable for living and places of business, industry, and other buildings as unsuitable, filtering or masking out the areas deemed unsuitable (Maantay et al., 2007). A complication with this approach is mix use buildings where commercial and residential reside in the same structure. Structures such as these are common in the recently gentrified areas of the city, along major artillery roads, and along natural features such as parks and waterfronts (Grant, 2002). Mixed-use development is the zoning of a building or a set of buildings to have more than more than a singular purpose- not solely residential or commercial space- rather a mixture of many uses. Mix use developments are created to spatially cluster employment, housing, commercial, and recreational activities together in a centralized urban space (Duaney, 2002). Mix use buildings and New Urbanism communities are developed to help eliminate some of the strain on the local transportation network. A collection of similar mixed buildings, or a New Urban District, is preferably spatially close to a public transit node (Grant, 2002). Mix use buildings are often the result of gentrified post industrial urban areas or as part of a planned town center. In specific zoning terms, mix use development refers to some combination of residential, industrial, office, commercial, and institutional land uses (Duaney, 2002). In the mix use building pictured below, small-scale commercial uses fill the street level and residential the

7 upper two floors. This type of structure is common in the redeveloped spaces of Chicago and adds a level of uncertainty to the personal space model. Figure 10-Mix Use Building, Lincoln Park Chicago This binary dasymetric approach will begin to counteract the generalizations and arbitrary boundaries of neighborhoods and census zones by assigning only specific buildings as suitable for living. Mix use buildings, in this step, are considered as suitable for inhabitance by residents. Later in the model mix use buildings will be divided so that 40% of the space will be assigned to non residential and 60% to residential. A limitation of the binary approach is that it assumes homogenous residential space in the buildings distributed across Chicago, and the model will assign a singular value to the space. This method will only deem a building as suitable to be included in the residential density formula, and does not account for variation

8 within buildings. This variable, whether the building is suitable or unsuitable for residential, is named residential buildings. Following this, an areal interpolation approach is used to allow for the transformation of a source data set into a target data set (Mennis 2003). This method is used to aggregate population values from the different zones to the target layers. In this case, the target layer is the summation of residential floor space within the lowest level of census measurement, the census block. This method takes the data within the specified zones from the source data- population data summarized- and aggregates this into the appropriate zones of the target data set. Specifically, this method will assign the population of each census block into the buildings deemed residential in the binary method. The summation of the livable area for each building is calculated with the product of the residential buildings classification, the area of the building footprint, and the number of stories for that building. A total livable space is calculated for each building, represented with a variable livable space. In the case of mix use buildings, 40% of the livable space will be assigned to non residential and 60% to residential, following the model used in development simulation experiments (Waddell, 2003). The population of the census block is assigned to the building based on what percentage of the cumulative livable space within the census block is the livable space of that building. For example, if one building accounted for 25% of the cumulative livable space of a census block, 25% of that blocks raw population numbers would be allocated to that specific building. Areal weighting is a simple interpolation method which will allocate the summarized population data according to the proportional area of the zones in the target data (Langford, 2003).

9 Each person within the block will be allocated a percentage of the total residential floor space within the boundary of the population data. The areal interpolation will again rely on the assumption that population is distributed uniformly within the target zones (Maantay, 2007), that the residential patterns within the building are homogenous. Obviously this is not true, but the level of measurement is constrained by the census data- in other words, the lowest level of census information, the census block, controls the scale of the project. The buildings can be mapped as a percentage of the total but individual building variation within the block cannot be achieved with this approach. This research is concerned with creating the most accurate and precise representation the population of the urban environment possible with census data- a detailed illustration of where and how people live. While having the before mentioned limitations, the use of a dasymetric technique will expose the limitations of the cartographic technique of choropleth mapping and the conceptual limitations of urban population density mapping. Moving beyond population density in the traditional sense, the amount of residential living square footage allotted to each person is calculated with this a measurement that can be described as personal space. The personal space measurement will show not how many people live in an area, but how people live within that area, how populations are distributed across the built environment of the modern urban space. A bivariate choropleth design will allow for the spaces in the city where density and crowdedness are confused to be illustrated.

10 3.2.3 Bivariate Legend The bivariate legend allows for spatial comparisons and for the emergence of spatial patterns in the differences between the traditional population density measurement and the personal space measurement at the city scale. Using a bivariate map illustrates the correlation between the traditional measurement and the new measurement, revealing areas of Chicago that are misrepresented by the traditional population density measurement. This legend is created by plotting the population density of every census block aggregated to every building within that census block on the x-axis and dividing that range into three quantiles. This will give each of the three classifications the same number of observations, essentially creating a high population density, medium population density, and low population density classification. The range of personal space is plotted on the y-axis and also divided into three quantiles. This creates a high personal space, medium personal space, and low personal space classification. The two classifications are combined together on a three by three grid and symbolized using diverging color schemes. The diverging color scheme in the bivariate legend of personal space and population density is applied to every building in Chicago and begin to illustrate where there is an interesting interaction between the two measurements.

11 The critical areas of this legend are the four corners- the green, purple, orange, and pink classifications. The green classification symbolizes places that have a high density and a high amount of personal space. A high population density suggests that there are many people living on the planar surface within the boundary unit of the census block. High personal space would suggest that the people living within this boundary unit are living in residential spaces that are above average in terms of amount of space per person. The green classification of buildings suggests that the traditional measurement of population density is insufficient in characterizing the lived experience of crowdedness or spaciousness in the living space of the built environment. Likewise, the pink classification illustrates buildings in low population density blocks where the amount of personal space is below average. Again, this classification illustrates a space where

12 the traditional measurement has failed to characterize the experience of crowdedness or spaciousness in the living space of the built environment. The purple classification shows areas where the population density is high and personal space is low. The orange classifications show areas where population density is low and personal space is high. The muted colors that form the cross in the middle signify the spaces in the city that are average in population density or personal space. The design of the bivariate legend is done so to illustrate the spaces where the traditional measurement of population density either adequately captures or fails to characterize the living spaces of Chicago in terms of the experience of crowdedness or spaciousness of personal residential space. The personal space metric and population density of the surrounding census block can be measured in each building in the city. Moving from the building level to the scale of the entire city, the representation of the bivariate space metric at each building becomes

13 obsolete. Rather, the most appropriate measure is to summarize the average amount of personal space per census block and, combined with the census block population density, display the bivariate choropleth map for the extent of Chicago. This method will essentially break down the census data to allocate the amount of residential space per person and then reconstructs it at the census block level for representation. The bivariate metric can be utilized all the way out to the community area level for a very broad overview of the spatial structure of this interaction. The allocation of this data to the community level, however, will rely on the boundaries that the measure itself is attempting to deconstruct and ultimately provides little insight. 3.3 Demographic Profiles of Chicago A primary purpose of the personal space measurement to is to evaluate the residential spaces in Chicago and gain a better understanding of how people are distributed across different spatial environments. In order to better understand this distinction and to explore the implications of the new measure, this section will examine how demographic distributions change when the definition of the space is changed. Demographic profiles of neighborhoods or classifications of neighborhoods are commonly used measures to evaluate the social environment of a space. The evaluation of the members of a contained micro-environment, such as a bounded neighborhood, allows for the conceptualization of the socio-economic influences and the socio-cultural features of a space (Wen et al, 2003). The use of census data to show that a certain percentage of a space is of one group and another percentage, a different group, is an essential element of the organizational framework of population analysis. This section will explore this concept and show the differences in racial classifications when the measurement population density is changed to personal space

14 Obtaining racial data would seem to be a straightforward process: the census asks a question; statisticians, demographers, and other properly trained professionals tabulate the responses (Nobles, 2000). This process however is not as basic as it would initially appear. In the Census form, respondents are given the choice to select multiple racial categories from the following list of options: White, Black or African American, American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific Islander, and Other (US Census Bureau, 2011). The Census forms list two ethnicities, Hispanic or Latino and Non-Hispanic or Latino. The Census Bureau defines Hispanic or Latino as "a person of Cuban, Mexican, Puerto Rican, South or Central American or other Spanish culture or origin regardless of race (US Census Bureau, 2011). For this research, I have divided the racial or ethnic self identification into five categories for analysis and representation: White, Black, Hispanic, Asian, and Other. To illustrate the differences in the changes in demographics as the value of personal space is changed; the comparison of high density spaces will be made with the high density, high space classification- green- and the high density, low space classification- purple. Similarly, the low density spaces will be contrasted with the low density, high space areas- the orange classification- and the low density, low space areas- pink. The comparison of the different spaces will show both percent of total population for the different classifications as well as raw population numbers. The demographic profiles are collected from the census block measurement. 3.4 Spatial Structure of Chicago Spatial Statistics Goals and Overview

15 The goal of this section is to employ spatial statistic tools and concepts in an exploratory manner to investigate the distribution of different classified census blocks on the bivariate map of Chicago. This section is exploratory in nature in that, rather than using spatial statistics to make concrete or absolute claims about the urban space and the people that inhabit them, the techniques are being used a tool to begin to understand how different classified areas operate in space and where would be the most apt place to focus qualitative and quantitative analysis will be in the future. The dataset for this section is a point pattern dataset from the city of Chicago that has 16,885 point features representing the centroids of each census block in the city of Chicago. The points are classified into nine classes based on a bivariate legend explained above- traditional population density measurement on the y axis and personal space measurement on the x axis. The main areas of interest in the analysis are the points that are classified in the four corners of the legend, the areas that represent the combinations of highs and lows in the classification- in this case the green, pink, purple, and orange classifications. The green represents areas of high population density and high amounts of personal space. The purple is low population density and high personal space. The orange classification is high density, low space and the pink low in both categories. The 16,885 point dataset for the entire city of Chicago required sampling for the nearest neighbor analysis. Nearest neighbor analysis works well up to 3,000 points; beyond 3,000 the measurement starts to break down and does not return consistent variables (Bailey & Gartrell, 1995) CSR Model

16 The first test will be testing whether each of the four corners of the bivariate classification, the four areas of interest, differ in their distribution across the city space from complete spatial randomness. This will indicate whether the spaces of interest from the bivariate model show a pattern of clustering beyond what would be expected from a random point pattern. The first step in this process is to calculate the nearest neighbor calculation on each of the four areas of interest. The null hypothesis for this experiment is that the spatial distribution of the classified census blocks is not clustered and is completely spatially random in location within the city boundary of Chicago. The next step is to simulate a completely spatially random dataset of 3000 points within the city of Chicago with n=39 simulations and calculate the nearest neighbor of each simulated point for each simulation. This is done to create a distribution of nearest neighbor results equaling a 95% confidence intervals (Bailey & Gartrell, 1995). This allows for a distribution for what a complete spatially random pattern would look like which can be compared to the each classification in an fhat-h plot. This will allow for the comparison of the different classified point patterns to determine if they are spatially not randomly across the space of Chicago Thomas Model After determining whether or not the dataset is completely spatially random, the next logical step is to formally test whether the four point patterns compare to a cluster model. Using the Thomas cluster model, this test will determine if certain areas of interest are significantly more clustered than the background population of Chicago census blocks. The purpose of this experiment is to determine if any of the point patterns are significantly more clustered than a fairly strong simulated cluster model using a Thomas cluster model with the size and intensity of

17 the cluster based on a sampling of all the blocks in the city. This approach this will illustrate the areas that are especially clustered while at the same time taking into account that the point pattern is derived from census blocks and an artifact of the census structure will be a gridded pattern. The null hypothesis is that there will be no clustering above what is expected from the background distribution of census blocks. By using the Thomas cluster model with a radius and intensity of cluster simulations based on the structure and natural clustering of census blocks, the gridded structure of the city can be accounted for and classifications that exceed expected clustering can be observed. The first step is to simulate a Thomas model dataset of 3000 points within the city of Chicago with n=39 simulations and calculate the nearest neighbor of each simulated point for each simulation. The intensity of the cluster is calculated using the rate of clustering from all the census blocks in a community area. This represents the natural clustering of the city s census block structure. The radius of the cluster is average length of a community area centroid to its boundary. The cluster model with the intensity and radius of the cluster set at this level is designed to replicate the underlying population of census blocks in Chicago. The model creates 39 simulations to create a distribution of nearest neighbor results at 95% confidence intervals Interaction Model The next test is an interaction model on all the area of interest point patterns against the other area of interest point patterns to determine if certain classifications attract or repeal other classifications. This analysis is performed multi-directionally to determine if one point pattern holds more weight in the repulsion or attraction interaction. This test will be performed specifically on the green, pink, purple, and orange classifications against each other in both

18 directions. Not all of the sets of points have the same number of observations. The following list shows the number of points each classification has: Green-1,238, Pink- 1,211, Orange- 2,826, and Purple-2,853. To alleviate any problems that may arise from different size samples, each classification has been randomly sampled to equal 1,211 observations. The interactions of point patterns will explain whether one event, the green classification for example, has a direct impact on the spatial structure a second event, the purple classification for instance. Both events occur in the same space, the city boundary area of Chicago, but it is unclear whether or not there is an association between the two. The null hypothesis is that all couplets of events will be independent of each other and not show significant signs of attraction or repulsion. For this test, there are two variables, event I and event J. The interaction method will test to see if the probability that the distance from a randomly selected object in event I is closer to which of the two point patterns. This is repeated for every point in the target event. For example, if testing the interaction of the green classification to the purple classification, each point in green is selected and a nearest neighbor analysis run to determine if the nearest point is of the green or the purple classification. This will determine whether the spatial distribution of the purple classification has a direct influence on the spatial distribution of the green classification. With the use of exploratory data analysis- the complete spatial randomness model, the Thomas cluster model, and the interaction model- the spatial structure of how the different classifications are distributed across Chicago can begin the be explored. Exploratory spatial statistics are a starting point for beginning to think about what types of social and historical processes in Chicago are driving the spatial interaction of different lived experiences in different built environments.

19 3.5 Dot Density Methods There are four main considerations when making a dot density map that must be considered in order to intelligently design the map with implying a misleading spatial distribution of the phenomena. One must consider the aggregated boundary units, the size of the dots, the observations per dot, and the location of the dots (Slocum et al, 2009). To understand as precisely as possible the residential patterns in the urban space, these considerations need to be narrowed in scope as much as possible. Dots should be placed in the smallest areal unit, the residential building, to increase the precession of the placement of the individual. Each dot should represent one person to increase the accuracy of the representation of the individual. To observe the most accurate map of how people occupy the urban space, the boundaries need to removed and the individuals represented in space alone. When making a dot density map, the smaller the polygon the dots are randomly placed within the more accurate their location will be to the location of the entity being mapped (Slocum et al, 2009). Ancillary information, in this case, the buildings zoned residential and the vertical extent of those buildings are used to as the target layer which dots will be placed in. The population of each individual building is determined by using a Poisson distribution based on the expected population of each building. The expected population for each building is derived by calculating the expected amount of space per person from the total population of the census block into the amount of cumulative personal space measured in the census block. The personal space measurement will create a measurement that quantifies the amount of residential space in each building per person, the inverse of that will be the amount of expected people per building. From the expected intensity, the Poisson distribution allocates individuals into the building to be

20 represented in a dot density map. This is done under the assumption that all buildings in the census block are not homogenous both in terms of numbers and in terms of racial breakdown. The Poisson method, in this case, will account for variation within the buildings and not give every building in the census block individuals based on the common value of average personal space. The dot density method for this series of maps will represent each individual in the city with a singular dot confined to the building the Poisson distribution estimates that individual to live. The dots will use a symbology in which the hue of the dot will represent one of the five census race categories- White, Black, Hispanic, Asian, or Other. The use of chorodots will allow for the representation of different attributes while maintaining similar size and spatial locations across all observations (MacEachren, 1990). The chorodot technique will allow for the representation of different groups of individual people filling the space, both the planar and the vertical spaces, of the built environment around them. The infrastructure of the urban space provides a spatial structure of individual residential behavior that operates not on the boundaries of neighborhoods or census blocks, but rather on the functionality of the residential environment. The representation of this phenomenon, individuals of different races confined to the buildings the model predicts them to live in will provide valuable insight into the settlement patterns across Chicago. 3.6 Intensity Methods The final methods are designed to use the distribution of people allocated to specific buildings to create two new maps that show the intensity of people and the intensity of space without the use of any administrative boundaries. Both maps are made with a kernel density

21 function to create, first a representation of the population of Chicago with the boundary units removed, and second, a representation of the degree of crowdedness in Chicago. This map is designed to model these two population features without relying on boundaries or arbitrary geographies to determine the areas of classification. The population intensity map shows the distribution of people across the planar surface of the city. While this method does not account for the vertical space of buildings, it does use the personal space measurement as a derivative to create the estimation of how many people live in each building. The kernel intensity method is designed so that the estimated population value for each residential structure in the city is accounted for. The kernel radius is a function of that intensity of the population in each building. The assumption behind this is that the more people in each building, the more communal space they will occupy and draw resources from when outside the residential structure. The kernel size function is designed so the population of the building does not have a huge impact of the kernel size, but does alter it slightly to account for this allocation of communal space- an indication of the perceived experience of crowdedness of the space surrounding residential structure. The kernel size is designed so that a single family home with few residents will have an impact of intensity to match that of roughly a size of a yard while the most populated structure in the city will have a kernel size of about half a city block. By having the size of the kernel as a function of building population, the population of each residential structure will have an impact on the micro-scale population intensity in the immediate area around the building, but the intensity of the total building population will be the driving force behind the population intensity map. This map shows the areas of high and low intensity of populations without the use of any administrative boundaries, but fails to account for the amount

22 of space each person has. This map is represented using a traditional heat map index with colors ranging from blue for low intensity to red for high intensity. The second map, the space intensity map, also employs a kernel density method with a constant kernel size of 100 feet in diameter. The range of personal space is normalized on a scale of 0-1 so that the density function will show the distribution of the personal spaces and not the larger numbers of square feet per person. This method is designed not to calculate the intensity of the number of people each building has, but to calculate the intensity of the space each person has. The space intensity map is representing the relative crowdedness or spaciousness of each building in the city without relying on administrative boundary enumerations. This map is represented using a heat map index with colors ranging from blue for low intensity of crowdedness to red for high intensity of crowdedness. Both the population intensity map and the space intensity map are exported into the Google Earth interface for seamless viewing and interactivity at multiple scales. By using the format of an interactive virtual globe, it is immediately noticeable how the intensity of population and space change based on the built environment and vertical dimension of buildings. Another useful feature of the Google Earth interactive display is the addition of a three dimensional model to show the vertical extent of the built environment. In a map of population or crowdedness with boundaries, the spaces that are non-residential would have the same value as those places where people live. There is no population that lives on a golf course. A park is not a spacious or crowded living space. Using this method shows a clear difference in how the spatial structure of the city changes the intensity of people and spaces without generalizations and the use of boundaries.

23 3.7 Summary The methods section of this thesis employs a variety of techniques in attempts to better describe and represent the phenomenon of modern urban residential life. The main focus with this method is working towards the deconstruction of the employment of boundaries in cartographic representations of urban space. The vertical space is a feature of urban residential structure that has not been accounted for with the traditional measurements of density and the representations of density with standard choropleth and dot density approaches. The personal space index and the bivariate legend are methods to model this vertical space as an active residential environment. The exploratory spatial statistic models are attempts to discover patterns across the space of Chicago of the personal space classifications. A fine scale dot density approach to allocate individuals and demographic characteristics of the individuals to the building level at a level of representation where each dot equals one person was performed to explore the microstructure of the built environment in Chicago. A kernel density approach was taken to represent the intensity of population and the intensity of crowdedness at various scales across the city without the use of boundaries. The maps created with the methods illustrated in this section have been placed in the virtual globe environment of Google Earth for seamless user interaction. The virtual globe environment allows for results to be observed at various scales set against the context of areal imagery of the city.