Statistical analysis of drainage density from digital terrain data

Drainage density (D_d), defined as the total length of channels per unit area, is a fundamental property of natural terrain that reflects local climate, relief, geology, and other factors. Accurate measurement of D_d is important for numerous geomorphic and hydrologic applications, yet it is a surprisingly difficult quantity to measure, particularly over large areas. Here, we develop a consistent and efficient method for generating maps of D_d using digital terrain data. The method relies on (i) measuring hillslope flow path distance at every unchanneled site within a basin, and (ii) analyzing this field as a random space function. As a consequence, we measure not only its mean (which is half the inverse of the traditional definition of drainage density) but also its variance, higher moments, and spatial correlation structure. This yields a theoretically sound tool for estimating spatial variability of drainage density. Averaging length-to-channel over an appropriate spatial scale also makes it possible to derive continuous maps of D_d and its spatial variations. We show that the autocorrelation length scale provides a natural and objective choice for spatial averaging. This mapping technique is applied to a region of highly variable D_d in the northern Apennines, Italy. We show that the method is capable of revealing large-scale patterns of variation in D_d that are correlated with lithology and relief. The method provides a new and more general way to quantitatively define and measure D_d, to test geomorphic models, and to incorporate D_d variations into regional-scale hydrologic models.     

Uncertain seas: probabilistic modeling of future coastal flood zones

ABSTRACT

Future sea-level rise will likely expand the inland extent of storm surge inundation and, in turn, increase the vulnerability of the people, properties and economies of coastal communities. Modeling future storm surge inundation enhanced by sea-level rise uses numerous data sources with inherent uncertainties. There is uncertainty in (1) hydrodynamic storm surge models, (2) future sea-level rise projections, and (3) topographic digital elevation models representing the height of the coastal land surface. This study implemented a Monte Carlo approach to incorporate the uncertainties of these data sources and model the future 1% flood zone extent in the Tottenville neighborhood of New York City (NYC) in a probabilistic, geographical information science (GIS) framework. Generated spatiotemporal statistical products indicate a range of possible future flood zone extents that results from the uncertainties of the data sources and from the terrain itself. Small changes in the modeled land and water heights within the estimated uncertainties of the data sources results in larger uncertainty in the future flood zone extent in low-lying areas with smaller terrain slope. An interactive web map, UncertainSeas.com, visualizes these statistical products and can inform coastal management policies to reduce the vulnerability of Tottenville, NYC to future coastal inundation.     

Terrain Pattern Recognition and Spatial Decision Making for Regional Slope Stability Studies

A terrain partition scheme is presented that allows the identification of regions with high landslide risk in natural terrain zones on the basis of geomorphometric criteria from moderate resolution DEMs. The key factor being the terrain segmentation to aspect regions (regions formed by points preserving the same aspect direction) instead of using an artificial regular-grid terrain partition scheme. The study area is in western Greece (NW Peloponnesus) whereas a moderate resolution digital elevation model with spacing 75 m is used. Landslide inventory analysis and knowledge conceptualization identified that the landslide susceptibility of a particular aspect region is high, if the mean elevation is low and the mean gradient is high. Each aspect region was parametrically represented on the basis of its mean gradient and elevation. The domain of each parameter was divided to seven slices (classes) on the basis of the observed density. Subsequent knowledge based mapping identified aspect regions with high landslide susceptibility for the following spatial rule: (a) “mean slope in class 6 or 7” and (b) “mean elevation in class 1 to 5”. Alternatively the rule is expressed as mean slope to be equal or greater than 15^∘ whereas mean elevation to be in the range 0 to 750 m. These identified zones correspond to regions where historical landslides occurred (populated coastal areas in the North) as well as to south regions (natural terrain zone) where no landslide record is available, because of the limitations posed by the natural terrain landslide mapping program in Greece. The presented terrain segmentation technique combined to the spatial decision-making process, provided both an object framework for integrating geomorphometric parameters and a method for landslide risk analysis in natural terrain zones.     

Updating the Vegetation Layer of the NZLRI National Database Using Satellite Imagery

This paper describes four methods of rapidly mapping vegetation using satellite imagery, for use in updating the vegetation layer of the New Zealand Land Resource Inventory (NZLRI). The visual interpretation method was tested in a 500 km² study area on the North Island west coast where 3 6 NZLRI vegetation classes occurred. Sixteen distinct groups of NZLRI vegetation classes were identified on Landsat Thematic Mapper imagery, and named “image classes”. Classes were identified by correlating ground data with image colour and texture and by using recognisable landform and cultural features. A limited number of vegetation changes have occurred since NZLRI mapping was first carried out. Updating the vegetation layer of the NZLRI requires recognising and mapping changes and modifying the database. Identifying distinctive groups of NZLRI vegetation classes on satellite imagery will facilitate this.     

Spatial transgression of new religious sites in Israel

Religion and the expansion of religious sites throughout the built environment have a long and conflict-ridden history. This paper examines the development of three controversial religious sites in Israel that have developed in recent decades in an effort to better understand the kinds of political, social, and locational circumstances that cause some new sites to be regarded as spatially transgressive. The three sites examined here are the Mormon Center in Jerusalem, the Baha'i Gardens in Haifa, and the Church/Mosque in Nazareth. The study is based primarily on 75 structured, open interviews with stakeholders and decision-makers.The broader aim of the paper is to generate a better understanding of the concept of spatial transgression through systematic investigation based on the methodology of “framing.” This methodology provides a comprehensive vocabulary for perceptions, referred to as “frames,” and offers a detailed and systematic typology of frames based on the literature and the empirical data (grounded research) of the case studies.The main findings fall within the three aggregated super-frames identified in the research: “Process,” “Values,” and “Issues.” Of these, the Process super-frame was found to be dominant in all three cases. Comparing the different frames in the three cases enabled us to identify the factors that influenced the transgression process. It also facilitated a better understanding of the different “stories” involved and the concept of spatial transgression, which was found to exist on a scale ranging from low to high intensity. This paper also proposes a framing typology that may prove useful for understanding and mapping similar cases elsewhere.     

基于分层策略和模糊推理的北方石质山区土壤厚度制图——以滦平县虎什哈流域为例

土壤厚度信息对土壤碳储量估算、水文-生态过程模拟等有着重要影响,但我国北方石质山区缺乏现势性好、分辨率高的土壤厚度分布数据及其快速获取方法。基于北方石质山区土壤厚度的分布特点,先将地貌信息和植被类型叠加生成制图单元,再根据每类单元的特征,针对性地选取地形参数和地表覆被参数作为指示土壤厚度空间分布的环境变量,结合少量土壤样点,依据模糊推理模型,构建了基于分层制图策略的土壤厚度空间推测方法。以河北省滦平县虎什哈流域为例,利用从ASTER GDEMs提取的地形变量和从我国环境减灾卫星影像(HJ-A)提取的地表覆被信息对土壤厚度进行了推测。结果表明,该方法精度较高,是利用免费地形和遥感数据进行低成本快速土壤制图的实用途径。     

A NUMERICAL INDEX OF PODZOL AND PODZOLIC SOIL DEVELOPMENT

A numerical index of soil development, the POD Index, was developed and applied to 723 pedons of United States soils that either exhibit, or are developing, Podzol (Spodosol) morphology. The index is determined solely from morphologic (field) criteria, and provides the first soil development index for Podzol and Podzol-like soils that does not use chemical data. The index assumes that pedogenesis and profile development in these soils produces the following morphologic changes; (1) the E (eluvial) horizon becomes “whiter,” (2) the B (illuvial) horizon becomes “redder” and “darker,” and (3) the number of B subhorizons increases. Results indicated that the index was useful for differentiating between non-Podzols and Podzols, and between Entic and Typic subgroups of Spodosols. A comparison of POD Indices for Spodosols of differing drainage revealed that maximum development occurred in wet soils (somewhat poorly drained), with minimal development on the driest sites. This finding is consistent with current theory on the effects of drainage/water table relations on Podzol development. Additionally, the index has usefulness in chrono-sequences of Podzol soil development [Key words: soils, Podzol, Spodosol.]     

Towards a Regionally Balanced Geographic Education Beyond Geography Class

Abstract

This contribution to the “Comments” section first introduces a metric designed to estimate the amount of attention given to different countries of the world in academia using Internet “term paper mills”. This metric is used to introduce a call for the incorporation of more geographic education regarding peripheral areas of the world into the broader college curriculum. Even as geography courses struggle to incorporate knowledge of many peripheral parts of the world, the rest of the university experience is continuing to reflect perceived “national interests.”     

Wireless Mapping,GIS, and Learning about the Digital Divide: A Classroom Experience

Abstract

The purpose of this article is to describe a capstone course in undergraduate student geographical research in which GIS and other geospatial tools were used to teach undergraduate students basic geographical principles. The course uses the “cooperative learning” pedagogical approach to address one of a number of client-supplied research projects, chosen on the basis of logistical difficulty, time, student ability, and project importance. In the connection of primary data with existing data, students confronted a number of important research issues such as mapping ethics, database design and management, time management, group dynamics, and research limitations.     

中国地理科学进展与展望——与美国地理学战略方向的比较(英文)

Understanding the Changing Planet: Strategic Directions for the Geographical Sciences(UCP),published by the National Research Council(USA),and its comments in The Professional Geographer propose that uppercase and plural "Geographical Sciences"(GS) is the strategic direction for geography in the next decade for better understanding of our rapidly changing planet. According to these comments,UCP valued technologies and tools excessively("task"),and did not pay much attention to methodology("discipline"). Actually,both"task" and "discipline" are geographical wings,especially in the time of "big science".Enlightenment from UCP and its comments is the strategic direction that should be balanced between "task" and "discipline",GS should be a three-dimensional construct of a disciplinary system,methodology,and technologies and tools,and this system should be scientific humanism based on scientific spirit and directed by humanism. During the last 60 years,Chinese geographers devoted themselves to GS,including practice and theory. Obviously progress and outlook are proposed as interdisciplinary GS,Earth Surface Sciences(ESS) and Geographical Construction(GC). The disciplinary system of GS is very complex,and is composed of such human knowledge domains as sciences,technologies,engineering,and philosophy. The main mission is to research the open,complex,and macro earth system(not only scientifically,but also humanistically),and one significant methodology is "comprehensive integration of qualitative and quantitative means"(CIQQM). At the same time,another changing direction in Chinese geography is Human-Economic Geography(HEG).     

The empty shell of the planetary: re-rooting the urban in the experience of the urbanites

ABSTRACT

This paper offers reflections on a body of work that has been produced under the label of “planetary urbanization”. This term has its roots in speculative work by French writer Henri Lefebvre in the late 1960s and early 1970s and has recently been popularized by a new generation of critical urban theorists. In this commentary, I propose that Lefebvre’s idea of planetary urbanization (and the aligned concepts “complete urbanization” and “urban society”) offer a way to think productively about post-capitalist possibilities. Making reference to early writings by Marx and Engels about communism and the end of human pre-history, I argue that planetary urbanization presents a terrain for liberation from the constraints of capitalist histories. Given that this terrain is currently defined by the domains of neoliberalism and climate change a new politics is necessary to unlock the possibilities of urban society.     

A Field Plan for Large-Scale Terrain Mapping

Abstract

Field work in geography often involves an exercise in which the student is required to make some type of map. Although most areas of the United States are well mapped, seldom are extremely large-scale (larger than 1:24,000) relief maps available. A method of contour-line mapping using small contour intervals and a large scale is appropriate in teaching several mapping principles and requires only a few simple tools and the use of elementary mathematics. Percent slope is established at uniform intervals along closely spaced traverses of the area to be mapped. Spot elevations are thus established from which contour lines can be determined. Accuracy in field-data collection and care in cartography will yield a very satisfactory map of terrain characteristics of small areas. Several concepts of maps and mapping are taught through direct student involvement.     

An integrated methodology for assessing soil salinization,a pre-condition for land desertification

Soil salinization is mainly an arid-zone problem leading to land desertification. It reduces soil quality and limits the growing of crops. The control of this problem involves inventorying, mapping, and monitoring soil salinity, which requires cost-effective, rapid, and reliable methods for determining soil salinity in the field, and rapid, specific data-processing methods. This paper shows the usefulness of an integrated methodology involving a hand-held electromagnetic sensor (Geonics-EM38) and the ESAP (Electrical conductivity or salinity, Sampling, Assessment and Prediction) software for assessing, predicting, and mapping soil salinity. The salinity of a 0.45-ha surface-irrigated plot was analysed by reading the EM38 at 161 locations, and by employing the ESAP software for calibrating the sensor, and predicting and mapping soil salinity at multiple depths. To calibrate the EM38 sensor, the electrical conductivity of the saturation extract (ECe) of 57 soil samples taken at 19 points was measured. The multiple linear regression (MLR) calibration model predicted ECe from EM38 readings with R² ranging from 0.71 to 0.95 for the multiple-depth profile. Furthermore, the MLR calibration model provided field range average estimates of soil salinity. Fifty-seven percent of the field had ECe values above 4 dS m⁻¹. The salinity levels and distribution in the root zone identified areas with inverted profiles, which revealed drainage problems. The integrated method presented is a breakthrough in the ability to accurately and rapidly assess soil salinity in agricultural lands.     

Bridging theory and implementation – Testing an abstract classification system for practical mapping by field survey and 3D aerial photographic interpretation

ABSTRACT

The abstract classification system Nature in Norway (NiN) has detailed ecological definitions of a high number of ecosystem units, but its applicability in practical vegetation mapping is unknown because it was not designed with a specific mapping method in mind. To investigate this further, two methods for mapping – 3D aerial photographic interpretation of colour infrared photos and field survey – were used to map comparable neighbouring sites of 1 km² in Hvaler Municipality, south-eastern Norway. The classification accuracy of each method was evaluated using a consensus classification of 160 randomly distributed plots within the study sites. The results showed an overall classification accuracy of 62.5% for 3D aerial photographic interpretation and 82.5% for field survey. However, the accuracy varied for the ecosystem units mapped. The classification accuracy of ecosystem units in acidic, dry and open terrain was similar for both methods, whereas classification accuracy of calcareous units was highest using field survey. The mapping progress using 3D aerial photographic interpretation was more than two times faster than that of field survey. Based on the results, the authors recommend a method combining 3D aerial photographic interpretation and field survey to achieve effectively accurate mapping in practical applications of the NiN system.     

北京城市意象空间及构成要素研究

本文通过照片辩认和认知地图调查试图对北京城市意象空间进行研究。结果表明：北京市的城市意象空间是天安门广场为中心，以长安街和二不、三环、四环路以及前门大街等道路骨架形成的网格状系统。该网状系统以二环路为界，划分为内、外两个城区。在内城区，在道路框架的 基础上，由地标、节点、功能区等要素共同组成城市意象；而在外城区，则只有部分地标要素起主导作用。行政区对于整个市区居民只有模糊的意象。综合起来看，影响北京城市意象空间的主要要素是道路、地标和节点。     

Assessing the need for evacuation assistance in the 100 year floodplain of South Florida

The main objective of this study is to assess evacuation assistance need in the 100 year floodplain of South Florida (Palm Beach, Broward and Miami-Dade counties) by examining select population characteristics of the floodplain inhabitants. Dasymetric mapping is used to redistribute block group level census data to homogeneous inhabited zones of 30 m × 30 m. Because the 100 year floodplain does not correspond to block group boundaries, this data redistribution increases the resolution and accuracy of the floodplain population and their social characteristics. Data on poverty, age, vehicle ownership and mobile housing units are obtained for each 30 m × 30 m zone in the floodplain and is aggregated to the block group level. It is then used to assess evacuation assistance need (based on volume of need as well as concentration of need) for the floodplain in each block group. Results reveal variations in evacuation need across the floodplain. “Age” is the main driver of evacuation need along the coast. “Poverty” is a factor inland, in both urban and rural areas. “Lack of vehicle ownership” contributes to assistance need in coastal and inland urban areas, but not so much in rural areas. “Mobile housing” is a factor in rural areas. Miami-Dade County has higher volume and concentration of poor households lacking vehicular ownership. Palm Beach and Broward counties, on the other hand, have a more dominant presence of elderly and of mobile housing. These results have important implications for local and regional evacuation planning in the event of a 100 year flood.     

HUMBOLDT AND THE HABITABILITY OF CANADA'S GREAT NORTHWEST*

ABSTRACT. Alexander von Humboldt's influence in British North America during the nineteenth century was filtered mainly through British imperial applications of “Humboldtian” sciences, including geomagnetism and biogeography. The best‐known examples include Edward Sabine and John Henry Lefroy, Royal Artillery officers who, during the 1830s and 1840s, transformed British North American outposts and territories, including Rupert's Land, into Humboldtian sites and regions in Great Britain's imperial “magnetic crusade.” Important groundwork had already been laid by John Richardson, who applied data accrued during John Franklin's overland Arctic expeditions during the 1820s to systematize Humboldtian inquiries into the habitability of Canada's Great Northwest. Despite both the relative decline of Humboldtian sciences by midcentury and Humboldt's own reservations about the political ramifications of his science, his “cosmic” outlook circulated in Canada to refine territorial expansionists' scientistic arguments justifying annexation of Rupert's Land after the monopoly of the Hudson's Bay Company expired in 1869.     

Geographic Information Technologies and the History of a Shoreline: The Case of Chapter 91 in New Bedford,Massachusetts

Abstract

This article discusses the use of geographic information technologies to assist researchers in the exploration of historical databases. The case study is a pilot project in which we used geographic information systems (GIS) and global positioning systems (GPS) to study the history of the Public Waterfront Act (the “Chapter 91” program), a policy designed to balance private property rights, public interest, and environmental protection in the Massachusetts tidelands. The issues discussed range from the role of GIS in society and its limitations as a representational tool to the ability of current GIS to deal with historical data and to manage temporal attributes.

     

Sources of Sediment in Lake Pepin on the Upper Mississippi River in Response to Holocene Climatic Changes

Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 ¹⁴C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation, snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America.     

月面形貌仿真设计及在嫦娥三号任务中的应用

月面形貌仿真可以为嫦娥三号着陆前地形建立及视觉导航仿真测试提供逼真的三维月面环境。利用分形随机算法并结合月面撞击坑与石块的数学分布模型,在实现月面数字地形的基础上利用纹理映射和纹理融合的方法为月面地形添加纹理,完成了月面逼真三维环境的构建。结合导航相机的外方位元素和光照条件,实现了对该仿真月面环境的模拟环拍,支撑了嫦娥三号发射前月球车导航相机数据获取、地形建立、通行代价图计算、月球车路径规划等遥操作任务过程仿真测试。测试结果表明,仿真月面三维地形具有良好的视觉效果,满足了巡视器导航相机测试验证对精细月面地形和纹理的需求,为导航相机测试验证提供了有效的月面形貌仿真数据。