非正式聚落快速增长下的城市蔓延

姆万扎是坦桑尼亚第二大城市，也是非洲发展最快的城市之一，近年来城市蔓延问题日益凸显。本文以遥感解译的姆万扎2000、2010、2015年3期土地利用数据为基础，运用GIS空间分析、用地增长弹性系数、景观指数等方法和指标，并结合实地调研和关键知情人访谈，分析了姆万扎2000年以来城市蔓延的空间特征及影响因素。分析结果表明：1）2000年~2015年间姆万扎城市以非正式聚落形式快速蔓延，建成区扩展速度和扩展强度迅速增加；蔓延主要占用裸地，其次是植被，侵占植被的速度迅速加快；2）城市蔓延主要沿3条主干道进行，属于“廊道式为主，填充式为辅”的扩展模式，形成指状的城市空间形态；建成区紧凑度逐渐下降，形状变得更加不规则；3）城市蔓延的主要区域和整体范围都在扩大，距离衰减特征明显,沿东南方向扩展强度最高；4）城市蔓延主要受到人口与经济增长、交通条件改善、土地制度问题及有效规划缺失等因素的影响。加强次干路和地方道路的规划和建设，制定及时、有效、符合地方背景的城市规划，是未来姆万扎控制城市蔓延的可能途径。

Urban sprawl under the rapid growth of informal settlements

The urban sprawl problem of Mwanza, the second largest city in Tanzania and among the fastest growing cities in Sub-Saharan Africa, has become increasingly prominent in recent years. Based on the land-use classification data(2000, 2010 and 2015), supplemented with field surveys, methods including GIS spatial analysis, elasticity ratio of urban land growth and landscape index were employed to study the pattern and influencing factors of urban sprawl for Mwanza. The findings indicated that: 1）Mwanza experienced rapid spatial growth mainly in the form of informal settlements during 2000 to 2015. Bare lands followed by vegetation were mostly occupied during the urban sprawl, and the encroachment on vegetation was accelerating. 2）The patterns of the sprawl mainly took place along the three major roads, and were dominated by corridor expansion, coupled with filling-up expansion, forming a finger-like urban spatial form. The compactness of the built-up area gradually decreased and its shape became irregular. 3）The urban sprawl showed obviously distance attenuation feature, and the expansion intensity was highest towards the southeast direction. 4）The urban sprawl of Mwanza was mainly influenced by the growth of the population and economy, the improvement of traffic condition, land system and the lack of effective planning. Strengthen the planning and construction of both secondary and local roads, and make timely, effective and context-based urban planning are recommended ways to curb further urban sprawl of Mwanza.