Some results on unilateral ARMA lattice processes

This paper presents several linked results on unilateral autoregressive moving average processes on a rectangular lattice. It is shown that axially symmetric two-dimensional quadrant processes must be separable. Exact forms for the inverse variance matrix are obtained in some cases, which allow exact Gaussian maximum likelihood estimation and simulation. It is shown that generating functions can be used for extrapolation. The herringbone simulation method is discussed.     

交易成本的空间异质性与城市体系形成演化机理研究

城市从本质意义上理解是集聚化交易的空间秩序或制度,城市体系的形成受到城市间制度竞争的影响.作为制度分析的重要概念,本文引入交易成本来分析城市的体系演化,并以“长三角”城市体系为例进行了实证分析.文章认为,城市体系的形成是制度竞争和生产力进步的结果,很大程度在交易成本的空间异质性与运输成本之间交互作用中得到反映.受此影响,城市体系一般经历离散发展阶段、城市体系发展期和城市体系成熟期,并且随着交易成本空间异质性的深度演化,城市体系也将经历从“低水平均衡—不均衡—高水平均衡”的周期性的反复演变.     

Urban heritage endangerment at the interface of future cities and past heritage: A spatial vulnerability assessment

Uncontrolled urban growth has been an increasing concern in many regions throughout the world. Generated by a natural tendency of population growth in relation to unsustainable land use, city sprawl has led to complex spatial developments that are creating both benefits to, and challenges for decision makers. A major problem inherent in the uncontrolled growth of cities is the threat to the fragile cultural and ecological heritage, which may escalate to permanent and irreversible damage as a result of factors such as environmental depletion and landscape decay. Using modern geosciences and spatial information technologies as predictive tools to analyse and forecast urban growth, a regional spatial decision system may be useful in order to provide seemly and timely information on the risk of overburdening the carrying capacity regarding the historico-cultural heritage at local and regional levels.The present paper develops a predictive toolkit for urban heritage in relation to urban cultural endangerment. This common problem is shared through many regions of the world and is increasingly jeopardizing fragile archaeological landscape due to urban pressure. In this sense, and to forecast an example of this common pressure, the Algarve is exemplified as a laboratory for testing this novel methodology, relying on a combined analysis of urban growth potential and threats to the abundant presence of archaeological heritage in the area. Our appro ach supports the paradigm of city growth in the context of a common agenda emerging from the Valetta Treaty, in which preserving the archaeological heritage is recognized as a key element for sustainable development. The study provides novel empirical results from the above mentioned modelling approach, with important lessons for the developing world. This paper proposes as such, an integrative spatial analysis methodology on the issue of historico-cultural endangerment, which is a new approach to comparative spatial analysis for decision making on urban heritage endangerment at the regional scale. Later, the discussion extends to a more conceptual level of urban planning by considering the questions: Is urban sprawl influencing the way we perceive cities? If so, are there positive advantages in the paradigm of urban growth and urban sprawl which might help us to protect past heritage while ensuring sustainable and modern cities?     

Implications of spatial and physical structures for ICT as a tool of urban management and development in Cameroon

Information and communication technologies (ICTs) hold enormous promise for development efforts in developing countries. However, the potential of ICTs remains untapped for reasons that are largely unknown in sub-Saharan Africa (SSA). This region has the lowest level of ICT penetration in the world. The need to understand impediments to ICT performance are therefore most urgent in this region. This paper seeks to address this need by identifying factors that inhibit the functionality of ICT as a tool for improving urban management. It analyzes two cities in the region, namely Douala and Yaounde, respectively Cameroon’s economic/cultural and politico-administrative capitals. The following three factors are shown to impede the functioning of ICT devices, hence urban management in these cities: colonial racial segregation policies, the colonial legacy of land use compartmentalization and the lack of unambiguous physical addresses for structures in the built environment. It is suggested that concerned authorities institute the following measures. 1] Establish an unambiguous addressing system reposed on the municipal governance structure and the country’s vehicle matriculation taxonomy. 2] Actively promote ICT as an element of national development. Finally, it presents some examples of efforts to improve ICT penetration and functionality from Senegal and South Africa.     

Network autocorrelation models with egocentric data

Network autocorrelation models have been widely used for decades to model the joint distribution of the attributes of a network's actors. This class of models can estimate both the effect of individual characteristics as well as the network effect, or social influence, on some actor attribute of interest. Collecting data on the entire network, however, is very often infeasible or impossible if the network boundary is unknown or difficult to define. Obtaining egocentric network data overcomes these obstacles, but as of yet there has been no clear way to model this type of data and still appropriately capture the network effect on the actor attributes in a way that is compatible with a joint distribution on the full network data. This paper adapts the class of network autocorrelation models to handle egocentric data. The proposed methods thus incorporate the complex dependence structure of the data induced by the network rather than simply using ad hoc measures of the egos’ networks to model the mean structure, and can estimate the network effect on the actor attribute of interest. The vast quantities of unknown information about the network can be succinctly represented in such a way that only depends on the number of alters in the egocentric network data and not on the total number of actors in the network. Estimation is done within a Bayesian framework. A simulation study is performed to evaluate the estimation performance, and an egocentric data set is analyzed where the aim is to determine if there is a network effect on environmental mastery, an important aspect of psychological well-being.     

Estimating Spatial Autocorrelation With Sampled Network Data

Spatial autocorrelation is a parameter of importance for network data analysis. To estimate spatial autocorrelation, maximum likelihood has been popularly used. However, its rigorous implementation requires the whole network to be observed. This is practically infeasible if network size is huge (e.g., Facebook, Twitter, Weibo, WeChat, etc.). In that case, one has to rely on sampled network data to infer about spatial autocorrelation. By doing so, network relationships (i.e., edges) involving unsampled nodes are overlooked. This leads to distorted network structure and underestimated spatial autocorrelation. To solve the problem, we propose here a novel solution. By temporarily assuming that the spatial autocorrelation is small, we are able to approximate the likelihood function by its first-order Taylor’s expansion. This leads to the method of approximate maximum likelihood estimator (AMLE), which further inspires the development of paired maximum likelihood estimator (PMLE). Compared with AMLE, PMLE is computationally superior and thus is particularly useful for large-scale network data analysis. Under appropriate regularity conditions (without assuming a small spatial autocorrelation), we show theoretically that PMLE is consistent and asymptotically normal. Numerical studies based on both simulated and real datasets are presented for illustration purpose.     

A simulation comparison on spatial Poisson mixed models

The statistical methods for analyzing spatial count data have often been based on random fields so that a latent variable can be used to specify the spatial dependence. In this article, we introduce two frequentist approaches for estimating the parameters of model-based spatial count variables. The comparison has been carried out by a simulation study. The performance is also evaluated using a real dataset and also by the simulation study. The simulation results show that the maximum likelihood estimator appears to be with the better sampling properties.     

区域一体化、地区专业化与趋同分析 —基于珠江三角洲地区9城市的实证分析

 《珠江三角洲地区改革发展规划纲要（2008-2020）》提出促进区域经济一体化和加快发展先进制造业。本文以珠江三角洲地区9市的制造业为例,通过衡量行业空间集中度和地区专业化水平指标,发现随着区域一体化进程加快,珠江三角洲地区制造业的发展已进入聚集与扩散并存的新阶段,各城市间制造业结构的差异性增强,地区专业化水平提高,但珠江三角洲地区东岸、西岸内部各城市间仍存在不同程度的产业同构性。同时通过对珠江三角洲地区9城市1993－2007年面板数据的回归分析,珠江三角洲地区确实存在σ-趋同和条件β-趋同。     

我国房地产价格区域互动的实证研究

本文采用广义空间动态面板数据模型（GSDPD）和2002第一季度至2010年第三季度省际面板数据分析了我国房地产价格的区域互动。实证结果表明,我国房地产价格互动存在空间滞后效应和时间滞后效应,且城镇居民可支配收入、信贷扩张、土地价格和房屋竣工面积是影响我国房价的重要因素。实证结果还表明,相邻地区之间房价的影响程度比其它不相邻地区之间房价的影响程度大,经济特征相似地区间房价的相互影响程度比经济特征不相似地区间房价的相互影响程度小。     

混交林对祥云新松叶蜂结茧空间格局的影响

在云南松树内,树冠投影圈及投影圈内各层次和各方向混交林地茧的聚集强度大于纯林;在树间,混交林地茧个体群分布的面积小于纯林,混交林是5株云南松约10m~2和20株云南松约40m~2,纯林中茧个体群分布的面积是7株云南松约14m~2和30株云南松约60m~2。混交林地相对茧口密度低于纯林,主要集中在 m-6与 m 之间,占50.00%。