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Learning to Think Spatially: GIS as a Support System in the K-12 Curriculum http://www.nap.edu/catalog/11019.html SPATIAL THINKING IN EVERYDAY LIFE, AT WORK, AND IN SCIENCE 87 was a tear in the continuity of the profile. For an area of rugged terrain therefore, Tharp could not see the shape of the seafloor by looking directly at the shipboard data. The actual display on the graphic recorded in the ship showed the fractional part of the acoustic travel time in seconds. The integer part of the travel time was not displayed directly, but had to be “book-kept” by keeping track of the upward and downward changes of sweep. In other words, every 0.5 second of travel time (200 fathoms) looks in the shipboard data exactly like 1.5 seconds of travel time (600 fathoms) and 2.5 seconds (1,000 fathoms). If the shipboard watchstanders did not bookkeep accurately, the water depth could easily be off by 400, 800, or more fathoms. To ensure that some of the outgoing acoustic energy traveled downwards toward the seafloor despite the rolling and pitching of the ship, echo sounders of Tharp’s era emitted a 60 degree wide cone of sound, rather than a narrowly focused beam. In steep terrain such as a mid-ocean ridge crest, the first returning echo might be from a point off to the side of the ship rather than directly beneath the ship. In that case a mass of overlapping “side echoes” could partially or totally obscure the vertical seafloor echo on the data record. The ship tracks that Tharp worked with were irregularly spaced opportunistic crossings of the central Atlantic rather than the results of a systematic survey. The gaps between ship tracks were often large (hundreds of kilometers) relative to the size of the features being mapped, requiring rather bold interpolation between tracklines. The ships’ navigation was by celestial navigation and dead reckoning. The charted positions of the ships could be off by miles in any direction. Consequently, the bathymetric data on crossing tracks often did not agree. The intellectual challenge was in one sense the problem to be solved. There was no conceptual framework with which to guide the eye toward detecting spatial patterns in the data. There were few expectations as to what might or even could exist. The processes by which seafloor morphology is formed were almost completely unknown. There was no way of knowing, at the beginning of the work, where or when the process would end, and there were few guides as to where to begin looking for pattern and meaning. One obvious source, continental geomorphology, was in fact misleading. As it turned out, seafloor morphology is shaped by quite different processes than those that dominate in continental settings, and as a result, there are no familiar land surface analogues for many seafloor bathymetric features. 3.7.5 Marie Tharp: A Skillful Spatial Thinker at Work In creating maps of the seafloor, Marie Tharp epitomizes the skillful spatial thinker at work. We can see many of the dimensions of skilled performance. In doing so, it is important to reemphasize the extent to which she worked with limited technological support. Many of the tasks that she undertook with paper and pencil would today be supported by technology. A skilled spatial thinker is capable of detecting spatial patterns and regularities from a sparse, discontinuous, and error-laden data set. Even today, it would be a challenge for a geoscientist, knowledgeable about the processes that shape seafloor morphology, to generate sensible seafloor contours from the scattered ship tracks that Tharp had available. A skilled spatial thinker can depict and interpret spatial information despite noisy, ugly data. Tharp literally saw through the masses of side echoes and navigation errors in her data set. Part of her success is a reflection of another component of spatial thinking. She could shift easily back and forth among different vantage points and representations of spatial data. Tharp’s raw data were profiles; her intermediate products were lines of tiny handwritten numbers; and her final products were maps and paintings. A skilled spatial thinker is also creative in terms of using or, more significantly, creating new representational modes to convey spatial data. When the U.S. Navy prohibited Heezen and Tharp Copyright © National Academy of Sciences. All rights reserved.
Learning to Think Spatially: GIS as a Support System in the K-12 Curriculum http://www.nap.edu/catalog/11019.html 88 LEARNING TO THINK SPATIALLY from publishing their data in the form of contour maps, they developed the physiographic diagram technique (Menard, 1986). A skilled spatial thinker can combine multiple kinds of spatial and nonspatial information. By having one of her helpers plot earthquake epicenter locations at the same spatial scale as her bathymetric maps, Tharp was able to extrapolate the location of the mid-ocean ridge axis to regions for which there was no bathymetric coverage available. A skilled spatial thinker must be capable of holding large amounts of spatial information in mind at one time and browsing through these data. The rolls of PDR data from which Tharp worked eventually filled every room of a very large house, but it seemed that she could remember what bathymetric features she had seen and, of equal importance, where she had seen them (M. Tharp, March 2001 interview, Oral History Project of the John Heinz III Center for Science, Economics and the Environment). The ultimate power of spatial thinking enables one to see connections between observable or inferred spatial patterns and distributions, on the one hand, and those processes that may have caused those patterns to come into existence, on the other. Tharp recognized that a continuous, symmetrical, steep-sided valley, co-located with abundant earthquakes, could be formed by rifting (extensional tectonics) as predicted by the then-new and controversial theory of seafloor spreading. In Marie Tharp, all of these skills were intertwined with a passion and determination to solve a problem that many of her colleagues did not even recognize. Spatial thinking is not the only characteristic that accounts for Marie Tharp’s success, but it is fundamental to the successful mapping of the seafloor. 3.8 THINKING SPATIALLY IN GEOGRAPHY: WALTER CHRISTALLER’S DISCOVERY OF CENTRAL PLACE THEORY 3.8.1 The German Tradition of Location Theory Throughout the nineteenth century and during the first half of the twentieth century, Germany was a—if not the—center of geographical scholarship. As a respected discipline, geography was strongly entrenched in the German university system. A long tradition of German scholars had defined many of the key ideas in the discipline: Alexander von Humboldt and the science of exploration; Carl Ritter and the concept of the region; Friedrich Ratzel and the study of anthropogeography; and Alfred Hettner and the idea of chorology (or regional differentiation). One branch focused on the idea of location theory. At its simplest, location theory asked: Why are things located where they are? It sought to answer the question by finding general laws that would explain spatial patterns of such things as agricultural production, based on Johann Heinrich von Thunen’s (1826) model of agriculture, and manufacturing, based on Alfred Weber’s (1909) theory of industrial location. In 1933, Walter Christaller (1893–1969) published a doctoral dissertation that added another strand to location theory, accounting for settlement patterns with his central place theory (Figure 3.31). The echoes of that remarkable discovery still play a role in geography, sociology, and planning today. For some, central place theory is emblematic of the spatial analysis approach to geography, an approach that seeks to understand and model the processes that give rise to patterns on Earth’s surface. For all scholars, however, the discovery of central place theory is an illustration of the power of spatial thinking in geography. This analysis draws heavily on an autobiographical essay written in 1955 (translated and reprinted in Christaller, 1972): “How I Discovered the Theory of Central Places: A Report About the Origin of Central Places.” Copyright © National Academy of Sciences. All rights reserved.
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