Simple Scan Tests for Spatial Clustering on a Square Lattice

Many data sets collected for study areas consist of data values collected on a square lattice or for a set of pixels. Remotely sensed data provide perhaps the most common example. Frequently, we wish to know whether there are subregions of the study area that exhibit spatial clustering. In this article, we suggest how an approach for finding spatial clusters may be combined with the common practice of using 3‐by‐3 and 5‐by‐5 smoothing filters or kernels to construct two simple and easy‐to‐implement scan‐type tests. A simulation experiment shows that the power of these tests to find clusters compares favorably with an alternative test that is more complicated. The tests use simulated data, changes in a remotely sensed image for a study region in Texas, and data about wheat yields. Muchas bases de datos que se recopilan para una zona de estudio, consisten en valores recopilados en una retícula cuadrada o en un conjunto de pixeles. Los datos obtenidos por sensores remotos son quizá el ejemplo más común. Frecuentemente deseamos saber si existen subregiones de la zona de estudio que exhiban agrupamiento espacial. En este artículo, sugerimos cómo una aproximación para ubicar agrupamientos espaciales se puede combinar con la práctica común de usar filtros de suavizado (kernels) de 3‐por‐3 y 5‐por‐5 filtros, para construir dos test tipo scan, sencillos y fáciles de implementar. Un experimento de simulación demuestra que el poder de estas pruebas para ubicar agrupamientos, se compara favorablemente frente a otra prueba alternativa, que resulta más complicada. Las pruebas usan datos simulados, cambios en una imagen de satélite para un área de estudio en Texas, y con data acerca de los rendimientos de cultivos de trigo. 研究区收集的许多数据集是由基于方格网和像素采集的数据值组成的,遥感数据可能提供了最常见的范例。通常,我们希望了解研究区的子区域是否呈现空间集聚特征。本文提出了一种如何发现空间集聚的方法,可以与采用3*3和5*5平滑滤波或核函数的普通试验相结合,构造两个简单且易于操作的扫描试验。模拟实验结果显示,这些试验在寻找聚集特征的性能上优于更复杂的可替换性试验。文中所用的仿真模拟数据来源于德克萨斯州小麦产量的多时相遥感影像。     

The Pendulum of Congressional Power: Agenda Change,Partisanship and the Demise of the Post-World War II Foreign Policy Consensus

Many scholars contend that Congress rarely matters in the realm of foreign policy. The source of this collective impotence is often explained by the weaknesses in congressional institutions vis-a-vis the president, as well as a general inability to respond effectively to a dynamic international political environment. We contend that the debate over congressional activism has not adequately addressed the role of agenda change. We analyze all roll call votes in the House of Representatives relating to the international affairs agenda between 1953 and 1998. We find that presidents have become significantly more likely to stake out positions on economic and trade issues as compared to other international issues. We also observe that presidential positions in the realm of foreign policy are increasingly characterized by interparty and interinstitutional conflict. While this increased conflict has dramatically decreased the president's ability to successfully pass executive priorities in foreign affairs more generally, presidential success on economic and trade issues has witnessed a significantly greater decline. We infer from these results that changes to the foreign policy issue agenda represent one important factor that has affected not only the incentives for political parties to participate actively, but also the willingness of Congress to challenge the president in the foreign policy debate.Asked one day whether it was true that the navy yard in his district was too small to accommodate the latest battleships. Henry Stimson (chair of the House Naval Affairs Committee early in the century) replied, 'That is true, and that is the reason I have always been in favor of small ships.'1Carriers have been, are and will be for the foreseeable future an absolutely essential part of our deterrence force…2John Warner, senator from Virginia, home state of Newport News Shipbuilding     

Chert sources and distribution patterns in the stone age of West Finnmark,North Norway: A preliminary view

A preliminary analysis of chert sources and distribution patterns in west Finnmark is described. Three small quarries and a fourth possible source area are situated on the coast west of Alta. Petrographic and geochemical analyses lend tentative support to the proposition that chert from these coastal sources was distributed inland during the Late Stone Age and Early Metal Periods.     

Urban Indians: Patterns and Transformations

For centuries American Indians have been an object of Western fascination. All too often this fascination has been an invented view of Indian people. This is especially evident with the recent movement of Indians to urban areas within the United States and Canada. Not only has this movement been ignored by society in general but it has also received almost no comment in the geographical literature. In this analysis the complex character of urban Indian communities is sketched, a variety of interpretations of these communities is outlined and the implications for planning and public policy are examined. The recent emergence of Indian organizations provides an innovative alternative for planning and public policy—cultural planning for urban redevelopment.     

Documentary Evidence and the Medieval Pottery Industry

EARLY in my study of the medieval pottery industry it became clear to me that, contrary to general belief, a reasonable body of documentary evidence bearing on the industry had survived, but that it would take some years to assemble and interpret. There is no corpus of documents from which to begin, for surviving evidence is not only scattered in a very wide variety of documents, but is also dispersed geographically in a number of local record repositories. It might seem sensible to delay publication until a larger proportion of this evidence has been studied, or at least to avoid analysis and generalization at this stage; but pottery and potters are of interest to archaeologists here and now, and there is nothing written on the industry save assemblages of unrelated facts, often strung together from widely different periods. An effort has, therefore, been made to assemble the material so far available into a coherent pattern. Since this is the first time that this has been done, the result will probably require drastic modification in a few years' time. If the interim report here presented stimulates others to prove it wrong, this paper will have achieved at least one of its purposes.¹     

ASSESSING THE PRODUCTS OF GOVERNMENT: WHAT GETS DISTRIBUTED?*

The literature on the provision and distribution of urban public services has recently stressed the study of impacts rather than outputs. Impacts are conventionally conceived as the final stage of an orderly production process. Benefits are produced only after impacts are achieved. This paper argues, to the contrary, that costs and benefits stem from each stage of the public service production process. Consequently, a focus on the impact stage alone can be grossly misleading.