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.”



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