Conceptualizing space and time: a classification of geographic movement.(Abstract)

ABSTRACT: In an increasingly complex and interactive world, the need to study, manage, and understand the critical interface between physical and human environments is becoming more urgent, precipitating technological advancements in the dynamic spatio-temporal capabilities of geographic information systems (GIS) and associated visualization and representational techniques. Such efforts require a thorough knowledge of the intrinsic characteristics associated with changes in space and time. A comprehensive understanding of the underlying dynamic structure associated with movement is necessary before accurate, integrative, and insightful analyses, explanations, and representations of complex, geographically dynamic phenomena can be performed. Using the logical subdivision method of classification, geographic movement is conceptualized by its abstract spatial and temporal components creating a matrix of 12 unique classes characterizing the form of movement. The organization is a simplified framework that offers a movement language with which to describe the movements associated with diverse geographic phenomena. Classifying geographic movement by its changes in time and space serves as a useful construct that facilitates the comprehension of the general ideas and principles intrinsic to geographical patterns and processes and provides a solid foundation for representing and understanding complex geographic phenomena.

KEYWORDS: Space, time, movement, classification, scale

Movement and Geography

Geographic explanation revolves around the spatial property of the phenomenon under investigation as space is an inherent feature in geography. Space is also naturally linked with time; the two are subjective and necessary conditions of sensory experience that are empirically defined only with respect to phenomena (Akhundov 1986). The dimensionalities of these inherent geographic properties interact with one another as they evolve and change across the landscape. Such transformations in space and through time occur across all scales and refer to the movement associated with geographic phenomena. Geographic movement, or spatial change of an object, is associated with virtually any geographic description, explanation, or analysis at some scale. Sometimes, geographical analyses involve the direct examination of the motion itself, such as daily trip pattern studies where personal use of time and space in an urban environment are examined. With others, spatial change may not be the subject of direct inquiry, but rather may be viewed historically in the examination of a phenomenon over time, as with the case of "moving regions." Conceptualizing the dynamic nature of a phenomenon as it evolves and interacts through space and time is a crucial principle in geographical understanding.

Traditionally, however, movement was not regarded as a significant integrating concept within the geographic discipline. It was viewed as a consequence or byproduct of something larger that is taking place. Theories of movement have, for the most part, been lodged under different headings, such as spatial interaction and migration theory. Focus has usually centered on the overall process of which motion is a part; that is, the "what," "why," and "where from," and "where to" of a subject that is moving. However, in recent years geographers have sought to understand the activities and movements on the Earth's surface that help to explain the distributions of humans and their works (Robinson 1976). In 1984, the Association of American Geographers (AAG) and the National Council for Geographic Education (NCGE) defined movement as one of five central geographic themes to be included in geographic education at elementary and secondary schools across the United States (Joint Committee on Geographic Education 1984).

As a dynamic function of many geographical analyses, movement is receiving increasing attention particularly in investigations involving geographic information systems, visualization, and cartography. A key element in this research is how to store historic and anticipated geographic data effectively so that one can trace and analyze changes in an area and ultimately do temporal modeling and simulation of geographic processes (Langran 1992; Peuquet and Duan 1995). The development of new and more powerful visualization tools such as computer animation and three-dimensional modeling has allowed geographers to better understand dynamic phenomena by incorporating change in space and through time with the use of movement, perspective shading, and shadows (DiBiase et al. 1992). Improvements to these computerized tools in their spatio-temporal capabilities have facilitated greater understanding of complex dynamic processes at multiple geographical scales. However, before a comprehensive conceptualizations of movement can be made, the individual components of motion must first be abstracted. Once the underlying attributes of geographic movement are more fully understood, then significant progress towards performing integrative and insightful analyses and visualizations of complex, spatially dynamic processes can be achieved.

The key to improved understanding of geographic movement is to transcend specific examples and to establish the significance of some general principles and concepts inherent to diverse geographic phenomena. As an important and useful generalization step in conceptualizing a subject matter, geographers have long relied on categorization to place order on a chaotic world. Using the traditional positivist approach to science, phenomena from all branches of geography are generalized by abstracting the movements associated with these events, occurrences, and processes. This conceptualization is presented as a paradigmatic classification that orders geographic phenomena by their spatio-temporal characteristics and is the first step in developing realistic visualizations and comprehensive GIS data models.

Classification in Science and Geography

Classification is a logical operation in which a genetic concept is divided into classes, based on the criterion of similarity of the objects entering into a class and on their differences from objects entering into other classes. As a type of "cognitive description," classifications may range from simple primary observations through to sophisticated descriptive statements (Harvey 1969). At one end of the scale, the act of classification may involve the simple giving of a name to a group of objects, whereby all objects are automatically classified into two classes, those possessing the attributes connoted by the name and those not possessing them (e.g., houses and non-houses). At the other end of the scale, classification may be used to devise a formal scheme for the grouping of a definite set of objects into an elaborate hierarchy of classes (e.g., land use classification) (Gilmour and Walters 1964). Classifications are widely used in the geographic discipline and have included land uses, towns, climates, soils, rivers, coastlines, economics, and above all, regions (Harvey 1969).

Harvey suggests that given a purpose and adequate information regarding the criteria to be used in classifying, objects can be assigned using two fundamentally different kinds of classification procedures: "classification from above," which refers to logical subdivision or deductive classification, and "classification from below," which refers to agglomeration or inductive classification (1969, p. 334). Agglomeration takes a number of individuals and assembles them, using one of a large number of techniques based on discriminatory analysis, into classes according to some grouping or clustering procedure. No assumptions are made, or need to be made, about the cause of the differences and similarities between the individuals grouped in the same class. Grouping similar observations is the reverse of subdividing them; only the perspective at the starting point is different (Abler et al. 1971).

Logical subdivision divides, in a series of steps, a population into groups according to stated criteria, often the presence or absence of two or more attributes. In subdivision, the genus is divided on some principle, consequently, a logical subdivision presupposes that there is some understanding of the system being constructed (Grigg 1965). Neither method is better; each is adopted for a particular kind of purpose (Gilmour and Walters 1964).

The function of positivist science is to develop generalizations and conceptual frameworks about reality, and the classification of phenomena is often the first step taken towards scientific explanation in the diverse branches of science. Classification helps us to come to terms with the issues related to a subject matter under study. In our attempts to rationalize why an event is taking place or what the implications resulting from a particular phenomenon are we must first arrange each observation in context with other events or objects with which it interacts. This activity involves the comparison of unique phenomena and the identification of the fundamental principles and characteristics inherent in the objects. In other words, we organize the phenomena in terms of the things with which we are already familiar. Building conceptual frameworks allows the identification of intrinsic characteristics and of similarities and differences among objects and may facilitate greater understanding of the relationships among diverse phenomena.

Geographic Movement

Explanation of geographic phenomena often involves the description of change. A phenomenon may change aspatially (e.g., the land use of a particular parcel of land is rezoned from agricultural to residential), spatially (e.g., annexation of an adjoining land parcel to an existing property), or in both attributes (e.g., subdivision of an agricultural parcel of land into 50 residential lots). When the characteristics associated with a geographic phenomenon change location, geographic movement has occurred. Physical processes such as glaciation and change of seasons are expressions of movement (Boehm and Petersen 1994). With human geographic phenomena, movement is purposeful and is often explained in terms of spatial interaction (Lowe and Moryadas 1975).

The movement of people, goods, information, and ideas is typically discussed in such terms as migration, trade and transportation, communication, and diffusion, respectively (Hardwick and Holtgrieve 1990). Whether alone or in combination, these phenomena involve changes in both the temporal and spatial dimensions. The importance each of these attributes has in the understanding and comprehension of the movement will vary with each geographic phenomenon, as well as with scale.

Space

Space is the basic organizing concept of the geographer (Blaut 1972); the spatial point of view is the …