Where PDENi = DENi/ DENi and DENi is the density of
land development. DENi equals to the amount of land
development divided by the total amount of land in the ith
buffer in the ith buffer in total of n buffer
The thematic layer of urban sprawl of each period was
obtained by the classification of multi-temporal satellite
images. The thematic layers of buffers were created
respectively based on the proximity to town centers using
the buffer functions of GIS. The overlay of the urban images
and the buffer images can capture the densities of urban
sprawl in each buffer With the help of GIS, the area of
land use under each buffer was found out.
Three typical urban sprawl patterns can be identified in the
city from the analysis The first type is concentrated (Low
Development) as represented by Hongmei. The second type
is Dispersed (Medium Development) as represented by
Dalang which exhibited some dispersal away from the town
center. The third type is Highly Dispersed (High
Development) as represented by Tangsha. It has an upward
increase in the density of land development and dispersal of
urban development away from the town center. There three
types of urban sprawl patterns can be reflected from the
Entropy. In the first type of urban sprawl (concentrated),
most of the land development is near the town center and
the entropy is relatively small. Area farther away format the
town center is not so favorable for land conversion and most
of the land development is carried out only with in the
distance very close to the town center. There is more spread
land development in the second type (Dispersed) .the
entropy is higher than that of the first type. For the third
type or urban sprawl (Highly Dispersed), land development
spreads over the urban fringe and to the surrounding rural
area and the entropy is the highest among the three types of
urban sprawl.