The rich historical dimension of regional geography is indispensable to an understanding of contemporary landscapes and societies. For example, the shifting distribution of economic activities inside U.S. metropolitan areas is a response to changing geographic forces as the ending industrial age gives way to its postindustrial successor. Those dynamics remind us again of the central role of spatial processes, the causal forces that act and unfold over time to shape the spatial distributions we observe today. In turn, these geographical patterns may be regarded as individual frames in a relentlessly advancing film. This, spatial organization at any given moment of time represents a point in a long process and is clearly related to what went before (as well as to what will develop in the future).

Emphasizing this central concern, historical geographers today approach their diverse sub discipline from a number of different (although not mutually exclusive) perspectives.

The first of these is the study of the geographic past, wherein earlier spatial patterns are reconstructed and compared for time periods that were crucial in the formation of the present regional structure. The raw materials for assembling these snapshots of the past come from many sources: historical maps, books, censuses, archives, and interviews of long-time residents of the study area. This approach can also be used to build evolutionary models of spatial organization: The four stage model of U.S. intraurban growth is a good example, with the structural pattern of each era shaped by its prevailing transportation technology.

The second perspective focusses on landscape evolution, the historical analysis and interpretation of existing cultural landscapes. This search for "the past in the present" takes a number of paths. The study of individual relics, such as Hadrians Wall, is one of them. Another is comparative regional analysis of landscape artifacts such as house types , which facilitates the mapping of cultural change.

A third approach to historical geography can be called perception of the past, the application of modern behavioral perspectives to recreate and study the attitudes of previous generations toward their environments. Migration decision making is of particular interest where it involved the acquisition of accurate spatial information on the "mental maps" of potential migrants. For instance, before the U.S. Civil War, the Great Plains area was widely perceived as part of a "Great American Desert," a myth that helped delay its settlement until the late nineteenth century. Abstractions are valuable, too; a recent example is Donald Meinig's analysis of symbolic historical landscapes, from which he derived three idealized American community types that still exert a powerful hold on residential preferences throughout the United States - the New England village, the small-town Main Street, and the California horticultural suburb. More formal modeling approaches exist as well, such as the time-geography perspective developed by the Swedish geographer Torsten Hagerstrand, in which allocations of time for performing tasks in space are measured and regionally analyzed.

One of the most active areas of historical-geographical research - which has effectively integrated various approaches to the subject -is the study of settlement geography, the facilities people build while occupying a region. Because these facilities usually survive beyond the era of their original functions, they often provide some of the clearest expressions of the past in the contemporary landscape. The colonial landscapes of the New World have received considerable attention, especially the layout of Spanish colonial towns in Middle America.

The layout of this urban settlement type is shown in Fig. 4-2, and its historical geographical significance is described by Charles Sargent: The morphology, or form, of any city reflects its past, and the clearest reflections are found in the street pattern, the size of city blocks, the dimensions of urban lots, and the surviving colonial architecture. In the typical Spanish American city, this colonial past is today on view in what is now the city core, commonly laid out in a gridiron of square or rectangular blocks subdivided into long, narrow lots along equally narrow streets.
 

The morphology of the Spanish American City:
This particular spatial pattern hardly came about by accident - it was decreed by royal regulations down to the smallest details of street, building, and central-plaza construction - and was repeated throughout Hispanic America (including former Spanish-controlled areas of the southwestern U.S. such as New Mexico). since most Spaniards were urban dwellers, it was hardly surprising that they chose to build towns in their colonial territories. But why this particular town form? The answer rests with that other major quality of an urban settlement - function.

The Spanish colonial town possessed several functions that were best suited to the compact, gridiron-street-pattern layout. It is often said that the threefold aims of the rulers of New spain were "God, glory, and gold." Because the main function of the settlement was administrative, town sites were chosen to maximize accessibility to regional trade routes and sources of tribute from local Indians. This control function also extended to the internal structure of the town: everything was tightly focused on the central plaza, or market square, under the watchful eye of government authorities in adjacent buildings. Another leading town function was expressed in the central role of the church, which always faced the plaza as well. The Roman Catholic Church sought to convert as many Indians to its faith as possible, and the easiest way to do this was to resettle the dispersed aboriginal population forcibly in Spanish towns, where the collection of tribute, the recruitment of mine workers, and the farming of land surrounding the town were also facilitated. Because of the gridiron street plan, any insurrections by the resettled Indians could be contained by having a small military force seal off the affected blocks and root out the troublemakers. The Greeks and Romans learned this lesson when they established far-flung empires, and the grid-iron tradition was passed down to their Mediterranean European successors. This idea even has modern applications: the battle for Saigon (a non-gridiron city) in the 1960s and 1970s favoured guerrillas who could move at will through twisting streets and alleyways, whereas the inner-city riots of 1967 in gridded Newark and Detroit were quickly squelched by the U.S. Army, which systematically surrounded and pacified block after block.