Spatial Distribution of City Tweets and Their Densities

Social media outlets such as Twitter constitute valuable data sources for understanding human activities in the virtual world from a geographic perspective. This article examines spatial distribution of tweets and densities within cities. The cities refer to natural cities that are automatically aggregated from a country's small street blocks, so called city blocks. We adopted street blocks (rather than census tracts) as the basic geographic units and topological center (rather than geometric center) to assess how tweets and densities vary from the center to the peripheral border. We found that, within a city from the center to the periphery, the tweets first increase and then decrease, while the densities decrease in general. These increases and decreases fluctuate dramatically, and differ significantly from those if census tracts are used as the basic geographic units. We also found that the decrease of densities from the center to the periphery is less significant, and even disappears, if an arbitrarily defined city border is adopted. These findings prove that natural cities and their topological centers are better than their counterparts (conventionally defined cities and city centers) for geographic research. Based on this study, we believe that tweet densities can be a good surrogate of population densities. If this belief is proved to be true, social media data could help solve the dispute surrounding exponential or power function of urban population density.     

Effect(s) of the “No-Same-Color-Touching” Constraint on the Join-Count Statistic: A Simulation Study

The join-count statistic is used to measure the tendency of polygons of a given map type to attract or repel polygons of the same or different map types. Yet in certain maps—for example, natural resources maps—it is often impossible for a polygon of a given type to touch another polygon of the same type. (This is the no-same-color or “No-Same-Type-Touching” (NSTT) constraint referred to in the title.) This violates an underlying assumption of the join-count statistic and may render its use to study certain spatial phenomena inappropriate—even for measuring spatial autocorrelation among polygons that are not the same type. This was explored using Monte Carlo simulation. For polygons of different types, it appears that results of the join-count statistic can be interpreted without any special consideration for the NSTT constraint provided there are a minimum of five to eight colors in the spatial system. For polygons of the same type, results can simply be ignored since it is known that no two polygons of the same type will touch.     

Differences in hi‐tech immigrant earnings and wages across Canadian cities

This paper examines the relative earnings and wages of immigrants working in the hi‐tech sector in Canada's cities. Between 1990 and 2000, a sizeable earnings advantage of immigrants over nonimmigrants employed in the hi‐tech sector evaporated, and this change was most noticeable in the largest cities. We use population census microdata to examine the geographical dimensions of this shift. After controlling for individual characteristics, we show that immigrants in the largest and tech‐intensive cities earn significantly less relative to nonimmigrants than those in midsized and smaller cities. We also present results comparing the hi‐tech immigrant wage and earnings gap for the five largest Canadian cities. The findings are consistent with the notion that geographic differences are an important component of the overall earnings gap between immigrants and nonimmigrants.     

A Socio‐Geographic Perspective on Human Activities in Social Media

Location‐based social media make it possible to understand social and geographic aspects of human activities. However, previous studies have mostly examined these two aspects separately without looking at how they are linked. The study aims to connect two aspects by investigating whether there is any correlation between social connections and users' check‐in locations from a socio‐geographic perspective. We constructed three types of networks: a people–people network, a location–location network, and a city–city network from former location‐based social media Brightkite and Gowalla in the U.S., based on users' check‐in locations and their friendships. We adopted some complexity science methods such as power‐law detection and head/tail breaks classification method for analysis and visualization. Head/tail breaks recursively partitions data into a few large things in the head and many small things in the tail. By analyzing check‐in locations, we found that users' check‐in patterns are heterogeneous at both the individual and collective levels. We also discovered that users' first or most frequent check‐in locations can be the representatives of users' spatial information. The constructed networks based on these locations are very heterogeneous, as indicated by the high ht‐index. Most importantly, the node degree of the networks correlates highly with the population at locations (mostly with R² being 0.7) or cities (above 0.9). This correlation indicates that the geographic distributions of the social media users relate highly to their online social connections.     

A Map Overlay Error Model Based on Boundary Geometry

An error model for quantifying the magnitudes and variability of errors generated in the areas of polygons during spatial overlay of vector geographic information system layers is presented. Numerical simulation of polygon boundary displacements was used to propagate coordinate errors to spatial overlays. The model departs from most previous error models in that it incorporates spatial dependence of coordinate errors at the scale of the boundary segment. It can be readily adapted to match the scale of error–boundary interactions responsible for error generation on a given overlay. The area of error generated by overlay depends on the sinuosity of polygon boundaries, as well as the magnitude of the coordinate errors on the input layers. Asymmetry in boundary shape has relatively little effect on error generation. Overlay errors are affected by real differences in boundary positions on the input layers, as well as errors in the boundary positions. Real differences between input layers tend to compensate for much of the error generated by coordinate errors. Thus, the area of change measured on an overlay layer produced by the XOR overlay operation will be more accurate if the area of real change depicted on the overlay is large. The model presented here considers these interactions, making it especially useful for estimating errors studies of landscape change over time.     

中国大城市贫困研究的多种测度与多层模型分析

基于六大城市住户调查数据,采用多种贫困测度和多层模型分析的方法,探讨中国大城市居民贫困状况及其影响因素。研究发现,大城市低收入邻里的贫困状况存在较大差异,其中广州、西安的相对丢失(relative deprivation)严重且低收入群体层级结构复杂,昆明的贫困深度大,而武汉财富集聚相对明显。贫困多层模型表明低收入邻里贫困的主要影响因素仍存在于个体层面,个体在家庭制度、市场制度、国家福利供应中所表现的特征影响了贫困发生率;城市贫困同时存在邻里效应,主要体现在邻里经济状况和贫困文化的影响作用;而城市间的贫困差异亦不可忽视。     

A Critical Comment on the Taylor Approach for Measuring World City Interlock Linkages

In the study of economic‐geographic structures, the shifting focus from the national state to the city and its region has highlighted the lack of reliable interurban data sets. The abundance of usable data sets on international structures and flows has no counterpart when studying interurban relations, which makes it hard to draw any extensive conclusions regarding the structure of world city networks. Instead of relying on available data sets, Peter Taylor has developed a method for generating data sets that, it is argued, can be used in research on the structure of the world city network. In this approach, actors are defined as cities with internal attribute service values, values reflecting the presence of different transnational service‐producing corporations in each city. The structural values between each pair of cities are then established by a mathematical formula based on the service value of each firm in each pair of cities. This procedure can be criticized on two accounts. First, although internal attributes on exceptional occasions can be used as a proxy and as a rough estimate for structural values, such studies must have a firm theoretical underpinning in order to be valid from a network‐analytical perspective. If not, such generated structural values become nothing more than a function of internal attributes, thus losing the whole basic idea of social network analysis. Second, the Taylor function used for generating structural values can be questioned. Why should a large presence of TNC offices in a pair of cities imply a larger city interlock link than would be the case between a high‐ranked city and a low‐ranked city, as the city with the larger service value probably serves cities with a lower service value with economic command, control, and support functions?     

Redundancy as an Index of Change in Point Pattern Analysis

Point pattern analysis based on concepts from information theory can go beyond existing techniques. Direct measurement of spatial form is achieved when Thiessen polygons are constructed around the points; in this scheme, each point's proportion of total area may be treated like a probability. Three information-theoretic indices are available for analysis of a distribution of such probabilities. Entropy is density dependent. Redundancy, defined as the difference between observed and maximum entropy, seems to avoid this problem when the number of individuals in a pattern exceeds twenty. Comparisons of prior and posterior redundancy provide an indication of change in overall pattern form. An information gain expectation reflects changes for each individual in a pattern. Here, point-area redundancy parameters are determined for Poisson-generated patterns, using a gamma distribution of polygon areas and a computer-generated set. An application to an urban crime problem illustrates the use of these parameters in the analysis of pattern change.     

The Location Choice of Employment‐based Immigrants among U.S. Metro Areas*

Abstract. This paper examines the initial location choice of legal employment‐based immigrants to the United States using Immigration and Naturalization Service data on individual immigrants, as well as economic, demographic, and social data to characterize the 298 metropolitan areas we define as the universal choice set. Focusing on interactions between place characteristics and immigrant characteristics, we provide multinomial logit model estimates for the location choices of about 38,000 employment‐based immigrants to the United States in 1995, focusing on the top 10 source countries. We find that, as groups, immigrants from nearly all countries are attracted to large cities with superior climates, and to cities with relatively well‐educated adults and high wages. We also find evidence that employment‐based immigrants tend to choose cities where there are relatively few immigrants of nationalities other than their own. However, when we introduce interaction terms to account for the sociodemographic characteristics of the individual immigrants, we find that the estimated effects of location destination factors can reverse as one takes account of the age, gender, marital status, and previous occupation of the immigrants.     

The Problems of Small Cities and the Policy of Stimulating Small-City Growth

The policy of activating small-city growth through industrialization has focused largely on further development of such cities since it was first formulated in the 1960s. The author suggests that not all small cities possess the requisites for further growth and that it is a mistake to view them entirely as a transitional form of settlement. According to this view, small cities have a role to play as rural service centers. The problem is viewed not so much the industrialization and further growth of small cities, but an improvement of living levels designed to reduce the present gap between the standards of living in large and small urban centers. Further research on small-city problems is urged, proceeding from past emphasis on industrialization prospects to broader analysis of socio-demographic needs and the steps required to preserve small cities as an integral element of unified systems of settlement.     

PARETO OR LOG‐NORMAL? BEST FIT AND TRUNCATION IN THE DISTRIBUTION OF ALL CITIES*

In the literature, the distribution of city size is a controversial issue with two common contenders: the Pareto and the log‐normal. While the first is most accredited when the distribution is truncated above a certain threshold, the latter is usually considered a better representation for the untruncated distribution of all cities. In this paper, we reassess the empirical evidence on the best‐fitting distribution in relation to the truncation point issue. Specifically, we provide a comparison among four recently proposed approaches and alternative definitions of U.S. cities. Our results highlight the importance to look at issue of the best‐fitting distribution together with the truncation issue and provide guidance with respect to the existing tests of the truncation point.     

A Combined Cluster and Interaction Model: The Hierarchical Assignment Problem

This article presents a new spatial modeling approach that deals with interactions between individual geographic entities. The developed model represents a generalization of the transportation problem and the classical assignment problem and is termed the hierarchical assignment problem (HAP). The HAP optimizes the spatial flow pattern between individual origin and destination locations, given that some grouping, or aggregation of individual origins and destinations is permitted to occur. The level of aggregation is user specified, and the aggregation step is endogenous to the model itself. This allows for the direct accounting of aggregation costs in pursuit of optimal problem solutions. The HAP is formulated and solved with several sample data sets using commercial optimization software. Trials illustrate how HAP solutions respond to changes in levels of aggregation, as well as reveal the diverse network designs and allocation schemes obtainable with the HAP. Connections between the HAP and the literature on the p-median problem, cluster analysis, and hub-and-spoke networks are discussed and suggestions for future research are made.     

Implementing Cleaner Production Programmes in Changzhou and Nantong,Jiangsu Province

Cleaner Production (CP) has been advocated worldwide as a strategy for companies to obtain environmental and economic benefits simultaneously. This analysis of how city‐level CP programmes were implemented in Changzhou and Nantong (Jiangsu Province, China) finds that both cities failed to meet the Province's targets to implement CP at all large‐ and medium‐sized companies by the end of 2000. Ineffective vertical control, weak inter‐agency co‐ordination, and lack of alignment between CP requirements and the core missions and operating procedures of implementing agencies have impeded CP implementation in the two cities. The relatively few successful CP outcomes at companies are based on the professionalism and skills of individual implementing agents. However, successes that rely exclusively on individual agents may not last, and thus institutional changes will be needed if the government's CP programmes are to lead to broader CP adoption.     

Recursive Algorithm for Determination of Proximal (Thiessen) Polygons in Any Metric Space

A new and recursive algorithm for determining proximal polygons is based on quadtree concepts. The algorithm can use any distance metric, and produces a quadtree of the image of the proximal polygons. This can be converted to vector form, or be incorporated directly into a quadtree-based geographic information system, in order to solve a number of closest-point problems. The algorithm can also produce the Delaunay triangulation, which is the dual of the proximal polygons. Empirically, the running time of the algorithm is proportional to the number of centers raised to the 1.6 power.     

Demographic Change,Differential Ageing,and Public Policy in Rural and Regional Australia: A Three‐State Case Study

This paper takes a differential demographic change in six rural settlement categories within rural and regional Australia as the starting point for the measurement of differential ageing using a Relative Ageing Index which compares ageing in sub‐populations with the national norm. The spatial units employed are 412 rural communities, approximated by social catchments each consisting of a country town and its surrounding dispersed population. The study covers the period from 1981 to 2006 and includes the rural areas of New South Wales, Victoria, and South Australia, excluding major cities, peri‐urban areas, and the remote rangelands. It examines demographic change and differential ageing in a selection of the rural settlement categories recommended for further analysis in the report of the ‘Demographic Change and Liveability Panel’, one of three advisory panels established in 2010 by the then Commonwealth Government seeking to develop a sustainable population strategy for Australia. Ageing profiles are produced for the whole study area, for the individual rural settlement categories, and for the urban and rural components within each category separately. Results show that differential ageing is least advanced in the ‘regional cities’, most advanced in the ‘sea change’, but of most concern in the agriculture‐based rural settlement categories where it exacerbates the effects of overall population decline. In all categories, ageing in the dispersed rural population element exceeded that of the urban component. Results emphasise the vital role of the ‘regional cities’ category in future public policy development supported by ameliorative and collaborative measures for their surrounding agriculture‐based communities.     

Do land use restrictions increase restaurant quality and diversity?

There is significant evidence that restrictions on residential land use reduce housing supply, increase house prices, and limit inflows of low‐income households. Local decision‐makers often argue that their efforts are mere attempts to preserve local amenities. We provide evidence that there is some truth to this claim: that residents of cities with more restrictions on land use appear to have access to higher‐quality and more diverse restaurants. In the process, we develop measures of restaurant quality based on organically generated data that, while strongly correlated with expert assessments, are more easily calculated at high frequencies and levels of geographic granularity.     

Regional Coverage Maximization: Alternative Geographical Space Abstraction and Modeling

Analysis results are often found to vary with the way we abstract geographical space. When continuous geographic phenomena are abstracted, processed, and stored in a digital environment, some level of discretization is often employed. Information loss in a discretization process brings about uncertainty/error, and as a result research findings may be highly dependent on the particular discretization method used. This article examines one spatial problem concerning how to achieve the maximal regional coverage given a limited number of service facilities. Two widely used geographical space abstraction approaches are examined, the point‐based representation and the area‐based representation, and issues associated with each representation scheme are analyzed. To accommodate the limitations of the existing representation schemes, a mixed representation strategy is proposed along with a new maximal covering model. Experiments are conducted to site warning sirens in Dublin, Ohio. Results demonstrate the effectiveness of the mixed representation scheme in finding high‐quality solutions when the regional coverage level is medium or high.     

Un classement multicritère des villes du québec pour favoriser la prise en compte de leurs différences

When it comes to making planning and development decisions, the concepts of small, medium-sized, or large cities are sometimes used to adapt public policies and instruments, or even to highlight challenges that are specific to certain categories of city. In this article, we take a look at the various dimensions that can be used to characterize cities, so as to empirically test a multi-criteria approach and build a typology of Quebec cities. Using an ascending hierarchical classification, we derive 11 classes of cities, whose conceptualization and graphic representation enable us to highlight their role and, in part, to localize their polarized area. This article complements and adds to works undertaken by other researchers over the last 20 years. Although it does not aim to propose specific changes to public policies and instruments, this article may serve to inform public decision makers in the development of such policies and instruments, and to enrich academic debates on the nature of small and medium-sized towns in particular.     

中国与欧盟产业强关联复杂网络系统的比较研究

基于投入产出表构建中国和欧盟细分产业的强关联网络,运用社会网络分析法从整体、子群及个体三个层级对中欧的产业网络进行比较分析,以探讨中国产业复杂网络发展趋势、规律以及阶段定位。研究发现：①产业强关联网络的发展具有显著规律性,欧盟产业强关联网络发展形态是中国的高级演化模式;②欧盟产业间的紧密度及群体聚集趋势均优于中国,但中国产业间的资源传输效率表现更好;③中国当前正处于分配性及生产性服务业与制造业换位的转型期,但尚未达到欧盟所处的以服务业高度集聚作为网络枢纽以带动全行业发展的成熟稳定期;④中国和欧盟的区块网络均呈现近似“核心-边缘”的等级层次结构,分块网络从“单核心”驱动向“双核心”共振驱动更迭,但欧盟比中国更早实现双核心驱动模式。