Specification of spatial models: A simulation study on weights matrices

The correct specification of spatial models, and especially the choice of the spatial weights matrix, represents a crucial decision for researchers using georeferenced data. However, few guidelines exist on which weights matrix is most appropriate in certain cases. This paper therefore (1) studies the sensitivity of testing and estimating spatial models with different weights matrix specifications and (2) formulates recommendations for researchers applying spatial models regarding model selection and weights matrix specification. The research is based on Monte Carlo simulations with synthetic data.

Resumen

La correcta especificación de modelos espaciales, y especialmente la elección de la matriz de pesos espaciales, representa una decisión crucial para investigadores que estén utilizando datos georreferenciados. Sin embargo, existen pocas recomendaciones acerca de que matriz de pesos es la más apropiada en ciertos casos. Por tanto este artículo (1) estudia la sensitividad de los ensayos y la estimación de modelos espaciales con especificaciones diferentes de la matriz de pesos y (2) formula recomendaciones para investigadores que estén aplicando modelos espaciales en relación con la elección del modelo y las especificaciones de la matriz de pesos. La investigación está basada en simulaciones de Monte Carlo con datos sintéticos.

     

GIS and spatial data analysis: Converging perspectives

Abstract. This article identifies some of the important developments in GIS and spatial data analysis since the early 1950s. Although GIS and spatial data analysis started out as two more or less separate areas of research and application, they have grown closer together over time. We argue that the two areas meet in the field of geographic information science, with each supporting and adding value to the other. The article starts off providing a critical retrospective of developments over the past 50 years. Subsequently, we reflect on current challenges and speculate about the future. Finally, we comment on the potential for convergence of developments in GIS and spatial data analysis under the rubric of geographic information science (GIScience).     

Spatial interaction modelling

Abstract. Spatial interaction (SI) is the process whereby entities at different points in physical space make contacts, demand/supply decisions or locational choices. The entities can be individuals or firms and the choices can include housing, jobs, production quantities, exports, imports, face-to-face contacts, schools, retail centres and activity centres. The first SI models can be grouped under the generic heading gravity models. Their main characteristic is that they model the behaviour of demand or supply segments, rather than that of individuals and firms. This article traces the development of these models from their inception in the early part of the twentieth century to the present. The key advances include the replacement of the gravity analogy by the more general concepts of entropy or information theory, a statistical framework commonly used in physics. With the arrival of the regional science paradigm over 50 years ago, a key challenge has been to broaden these models compared to those arising in spatial economics, thus arriving at a more inclusive probabilistic framework. These efforts are discussed here, as well as inclusion of geographical advances, embracing activities as generators of travel, time-geography, recognition of spatial interdependencies, and use of neuro-computing principles.     

Spatial autoregressively distributed lag models: equivalent forms, estimation, and an illustrative commuting model

A spatial generalization of the (well-known special case from times series) Autoregressively Distributed lag model is defined. Equivalent forms—a Spatial Error Correction model, a Spatial Bewley model, and a Spatial Baardsen model—are considered. As none of these are consistently estimated by Ordinary Least Squares, an Instrument Variable estimation procedure is investigated using Monte Carlo simulation. It is found that there is a tendency to biased estimation results if the spatial autoregression is extremely low or extremely high. Finally, an empirical case illustrates the concepts discussed.     

A test strategy for spurious spatial regression, spatial nonstationarity, and spatial cointegration

Abstract.  A test strategy consisting of a two-step Lagrange Multiplier test is suggested as a device to reveal spatial nonstationarity and spurious spatial regression. It is further illustrated how the test strategy can be used as a diagnostic for presence of a spatial cointegrating relationship between two variables. Using Monte Carlo simulations it is shown that the small-sample behaviour of the test strategy is as desired in these cases.     

A global search procedure for parameter estimation in neural spatial interaction modelling

Parameter estimation is one of the central issues in neural spatial interaction modelling. Current practice is dominated by gradient based local minimization techniques. They find local minima efficiently and work best in unimodal minimization problems, but can get trapped in multimodal problems. Global search procedures provide an alternative optimization scheme that allows to escape from local minima. Differential evolution has been recently introduced as an efficient direct search method for optimizing real-valued multi-modal objective functions (Storn and Price 1997). The method is conceptually simple and attractive, but little is known about its behavior in real world applications. This article explores this method as an alternative to current practice for solving the parameter estimation task, and attempts to assess its robustness, measured in terms of in-sample and out-of-sample performance. A benchmark comparison against backpropagation of conjugate gradients is based on Austrian interregional telecommunication traffic data. Received: 11 November 1998 / Accepted: 14 January 1999     

深基坑工程实例及系统开发

对选定的武汉地区基坑工程实例,从场地周边环境、工程地质水文地质条件、支护方式、地下水处理方式以及监测数据等多个方面提取实例特征,考虑基于实例推理技术的要求,提出了能描述该地区基坑工程特点的数据结构,设计了新的C 类,实现了实例的输入、修改、存取和显示等功能,并应用于实际工程中。     

从摇篮到摇篮—建筑的理念·建筑设计的复兴·新一代建筑师

本文通过参考过去的以及实际上再创造的建筑思考和建造行为,将目前所需、面临的挑战和选择延伸为C2C理念,以期应对气候问题。     

低碳、高氮磷城市污水的化学辅助除磷研究

对于低碳、高氮磷的城市污水，可采用生物脱氮并辅助化学除磷的工艺进行处理，以使氮、磷同时达到排放标准。选择聚合硅酸铁作为混凝剂并将其直接投加到生物反应器中，结果表明，当投加量为12mg／L（以Fe计）时出水中的TP〈0．5mg／L，达到了《城镇污水处理厂污染物排放标准》（GB 18918-2002）的一级A标准。所投加的聚合硅酸铁与进水中TP的物质的量之比同出水TP之间具有很好的相关性，因而在进、出水TP浓度一定的情况下。可据此确定混凝剂的投量。投加了混凝剂后，污泥絮体变得更密实，沉降性能良好。     

Inferring migration flows from the migration propensities of infants: Mexico and Indonesia

The need for methods of indirectly estimating migration flows is particularly important in developing countries, where migration data are often incomplete and inaccurate. This paper focuses on the use of an indirect internal migration estimation method applied to Mexican and Indonesian census data. It shows that the mobility propensities of infants can be used to infer the corresponding propensities of all other age groups. However, the promise of this method is reduced in instances of inadequate data, and great care must be taken to identify outlying values in the data and to correct obviously erroneous patterns. Future work increasingly will be directed to this issue.     

On the idea of ex ante and ex post normalization of biproportional methods

Biproportional methods project a matrix A to give it the column and row sums of another matrix; the result is R A S, where R and S are diagonal matrices. As R and S are not identified, one must normalize them, even after computing, that is, ex post. This article starts from the idea developed in de Mesnard (2002) – any normalization amounts to put constraints on Lagrange multipliers, even when it is based on an economic reasoning, – to show that it is impossible to analytically derive the normalized solution at optimum. Convergence must be proved when normalization is applied at each step on the path to equilibrium. To summarize, normalization is impossible ex ante, what removes the possibility of having a certain control on it. It is also indicated that negativity is not a problem.Received: October 2002/Accepted: June 2003     

Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances

The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood (ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding in large samples, while the FGS2SLS estimator remains computationally feasible in large samples. Received: 20 January 2001 / Accepted: 31 August 2001     

C80自密实混凝土研究

优化配比参数，使用普通原材料配制出C80高性能自密实混凝土；通过掺入微膨胀剂。有效解决了高强自密实混凝土中因胶凝材料用量大而引起的收缩；进一步研究了高强自密实混凝土的工作性能、龄期强度及耐久性。分析讨论了影响混凝土性能的因素。     

基于基本回路分析法的热水网路水力计算软件

本文给出了热水网路水力工况的数学模型,采用了相应的算法基本回路分析法,并应用C Builder语言编制了热水网路水力工况计算的可视化程序,可以作为供热工程的教学辅助软件,同时也可以为实际热网水力工况分析提供有价值的参考.