Physical factors: Elevation and slope both showed significantly
negative effects on urban expansion in Beijing, indicating that the
steep and elevated areas were less likely to be developed. The
negative effects of slope on urban expansion have been observed all
over the world (Dubovyk et al., 2011; Ye et al., 2011). The reason for
this negative effect may be that the development cost in these areas
is higher than that in flat areas. In contrast, the effects of elevation
on urban expansion depend on the topography of the studied area.
Higher elevation usually restricts urban expansion because the
development of areas at higher elevations may be more costly.
However, positive effects of elevation on urban expansion have
observed in Lagos, Nigeria because drainage is needed in areas with
low elevation, which may increase the cost of land development
(Braimoh & Onishi, 2007; Dewan & Yamaguchi, 2009).