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Top1. Introduction
In the second half of the twentieth century, urbanization has taken place around the world at an unprecedented rate. During this process, natural lands have been rapidly transformed to urban lands, and urban population has rose significantly. As an example, only 29% of the world population lived in urban areas in 1950, and this ratio increased to 49% in 2005. Moreover, it is predicted that this trend is likely to continue (United Nations, 2006). Further, according to the United Nations population division report in 2002, the number of large urban agglomerations almost tripled from 1950 to 1975 and nearly doubled from 1975 to 2000 (United Nations, 2002). The report also states that by 2015 the number of large urban agglomerations (cities having urban population more than five million) will go up to 58 from 39 in 2000 (United Nations, 2002). Apart from economic opportunities, the internal growth and restructuring of cities, emigration, and demand for more living space are the major reasons behind the spreading of urbanized areas, which would likely lead to the formation of Gigalopolises (Clarke & Gaydos, 1998).
In the United States, urbanization is often associated with people moving out of cities and living in rural urban fringes, leading to a unique phenomenon termed as urban sprawl. Economic opportunities, better infrastructure, and preferences for natural landscape often drive people to move out of cities and live in these rural urban fringes broadly referred as sub-urban, ex-urban, or peri-urban areas. In particular, the presence of aesthetically attractive natural landscapes (Archer & Lonsdale, 1997), agricultural open space (Ready & Abdalla, 2005), and environmental amenities (Cho et al., 2005) have strongly affected residential decisions. During the process of urbanization, the losses of agricultural lands have been a major concern to scientists. In the United States, for instance, it was found that approximately 11 million acres of croplands were converted to urban lands between 1982 and 1997 and approximately one third of this conversion occurred on prime farmlands principally in the Western United States (Greene & Stager, 2001). In another example, in the Lake States of Michigan, Minnesota, and Wisconsin, it was found that since 1950s, forest, crop, and pasture lands have decreased by 3.2, 5.4, and 4.0 million acres respectively (Mauldin et al., 1999). In addition to the loss of agricultural lands, urbanization has many other adverse societal and environmental effects. For instance, accelerated urbanization leads to the increment of impervious surface area, and helps transporting and accumulating non-point pollutants via surface runoff (Xian et al., 2007). Further, the increased usage of motorized transportation, a result of urban expansion, leads to higher energy consumption and greater pollution. Because of these associated issues, understanding the dynamics of urbanization is a prerequisite to support comprehensive urban planning and management (Cheng & Masser, 2004).