单选题 Our understanding of cities in anything more than casual terms usually starts with observations of their spatial form and structure at some point or cross-section in time. This is the easiest way to begin, for it is hard to assemble data on how cities change through time, and, in any case, our perceptions often betray us into thinking of spatial structures as being resilient and long lasting. Even where physical change is very rapid, this only has an impact on us when we visit such places infrequently , after years away. Most of our urban theory, whether it emanates from the social sciences or engineering, is structured around the notion that spatial and social structures change slowly, and are sufficiently inert for us to infer reasonable explanations from cross-sectional studies. In recent years, these assumptions have come to be challenged, and in previous editorials I have argued the need for a more temporal emphasis to our theories and models, where the emphasis is no longer on equilibrium but on the intrinsic dynamics of urban change. Even these views, however, imply a conventional wisdom where the real focus of urban studies is on processes that lead to comparatively slow changes in urban organization, where the functions determining such change are very largely routine, accomplished over months or years, rather than any lesser cycle of time. There is a tacit assumption that longer term change subsumes routine change on a day-to-day or hour-by-hour basis, which is seen as simply supporting the fixed spatial infrastructures that we perceive cities to be built around. Transportation modeling, for example, is fashioned from this standpoint in that routine trip-making behavior is the focus of study, its explanation being central to the notion that spatial structures are inert and long lasting.

单选题 We, according to the passage, tend to observe cities______.

单选题 We think about a city as______.

单选题 Cross-sectional studies show that cities______.

单选题 The author is drawing our attention to______.

单选题 The conventional notion, the author contends,______.