中国城市形状的时空变化

基于国家资源环境数据库动态土地利用数据,计算了1990年和2000年我国31个大城市的形状指数.结果表明,从1934年～1990年的56年间城市形状从紧凑趋于非紧凑、分散;而在1990年～2000年10年间,由于受到城市建设用地控制增强的影响,城市形状趋于紧凑.从1934年～1974年间,在20个可比较的城市中有14个城市形状指数增加、6个城市形状指数减少.从1974年～1990年间,在22个可比较的城市中各有11个城市的形状指数增加和减少.从1990年～2000年间,31个城市中有11个城市的形状指数增加、20个城市形状指数减少.一些城市的形状指数在不同时间段变化十分剧烈.例如,兰州市是在1934年～1974年间形状指数增加最多的城市,而在1974年～1990年阶段则形状指数减少最多的城市.同样,武汉和昆明则是在1974年～1990年阶段形状指数增加量最大的城市,而在1990年～2000年阶段则是形状指数减少量最大的城市.这或许说明在城市规划和城市建设中,有时人们还未真正认识到城市形状的重要性,往往只有当城市形状变化到严重地影响人们的生产、生活和环境时,才发现形状存在的缺陷.

Spatial-Temporal Changes of the Shapes of Chinese Cities

Although there is still a dispute about the performance of the Boyce-Clark shape index, as a quantitative method for measuring the shape, the Boyce-Clark shape index is a good one in that it can present the general character of city shapes through the experiment. Shape indices of 31 Chinese cities at 1990 and 2000 were computed by the Boyce-Clark shape index method based on the dynamic land-use data from the National Resources and Environmental Database established by the IGSNRR, CAS. According to Lo (1980), the range of shape indices for Chinese cities varies from 10.410 to 40.620 in 1934, 16.170 to 73.070 in 1974, 13.004 to 69.902 in 1990 and from 12.687 to 116.398 in 2000. Chengdu is a city persisting the square shape with the shape indices of 10.550, 16.170, 13.004 and 14.144 in those four years respectively. The averages of the index in the four years are 23.950, 27.090, 32.507 and 31.507 respectively. It was found that, in general, shapes of Chinese cities tended to be less compact in the period from 1934 to 1990, while more compact in the period from 1990 to 2000, and it is perhaps a result of strong control to urban sprawl at the latter period. Generally, city shapes suggest the persistence of square or rectangle shapes from 1934 to 2000, although some cities also experienced linear development in the period from 1990 to 2000. Out of 20 cities, 14 cities showed a decreased trend in shape indices and six cities showed an increased trend from 1934 to 1974, and out of 22 cities, 11 cities' shape indices decreased and the rest had increased shape index from 1974 to 1990. Moreover, shape indices of several cities have been drastically changed during the period from 1934 to 2000. Lanzhou is a city with a highest increment in shape index (41.810) during 1934 to 1974, and a highest decrease (16.753) during the period from 1934 to 1974. Wuhan and Kunming are the first two cities with a high increment of 28.512 and 26.845 respectively in shape index from 1974 to 1990, but a high decrease of 15.571 and 17.615 respectively in shape index from 1990 to 2000. It means that city shapes are not considered by urban planners and managers as important issues until some urban problems such as heavy traffic and environment pollution appear to affect the life and work of urban inhabitants, therefore city shape is an important issue in urban spatial planning.