城市地域空间扩展情况是衡量城市化水平的重要测度指标。利用陆地卫星MSS影像、TM（或ETM＋）影像、灾害监测星座数据和“北京一号”小卫星数据,对1973—2005年北京市建成区的扩展过程、面积变化和土地利用影响进行了监测分析。结果表明：32年间,北京市建成区面积净增加超过1000km2,2005年达到1209.97km2,相当于1973年的6.58倍,年均扩展32.07km2。北京市建成区的扩展基本上呈现出以旧城区为中心向四周扩展的方式,并未在某一方向表现出特别明显的变化,但在不同时期内的扩展速度差异非常明显。北京市建成区的扩展面积中,54.34%来自于农村居民点和独立工矿用地及其他建设用地,43.57%来自于水田、旱地等耕地。人口增长对北京市建成区的扩展有显著的刺激作用;经济增长是城市变化的主要动力之一;交通的发展促进了城市用地的扩展,是城市扩展的牵引力,对城市空间扩展具有指向性作用;而政策与制度因素则在很大程度上决定了北京市发展和扩张的宏观格局。

The urban area expansion is an mi portant indicator formeasuring urbanization leve.l Based on three LandsatMSS mi ages, tenTM mi ages, oneDMC data and one“Beijing-1”small satellite data obtained in 2005, the urban built-up characteristic ofBeijing and its mi pacton the peripheral land during1973—2005were analyzed. The urban areawas183·84km2in 1973 and increased to1209·97km2in 2005, the built-up areawas increased by 1026·13km2during the past 32 years and expanded 32·07km2per year. The built-up area was expanded around the old area and didn’tpresentmanifestchange in a certain direction. The expansion ratewas distinct from each otherandBeijing citywas experienced two fastexpansion stages comparatively. The increased built-up area originated from different land use type, ofwhich about 54·34% converted from rural area and dependent factory, diggings land and other construction area. The othermainly came from arable land that account for43·57% of thewhole added built-up area. Many factors contributed to the urban land use changes.But fourmajor driving forces, population growth, economic increase, transportation infrastructure mi provement and institution and policy change, were themost mi portant factors. Population growth can smi ulate the built-up areamanifestly, the economic increasewas themain mi petus of the land use, the transportation infrastructure\nmi provementwas the mi petus for the urban expansion, while policy change determined the macroscopical development and expansion pattern in some degree.