Study on the Radiation Effect of Urban Spatial Expansion in an

Oasis: A Case Study of Ganzhou District in Zhangye City

Xuebin Zhang

1,*

and Jun Luo

1, 2

College of Geography and Environmental Science, Northwest Normal University, China;

College of Resources and Environmental Science, Gansu Agricultural University, China.

Email:zhangxb428@163.com

Keywords: Radiation effect, urban spatial expansion, oasis

Abstract:

The spatial expansion of oasis cities and towns is restricted by water resources; therefore, spatial expansion

in oasis has a greater impact on landscape than general towns. The article takes a typical oasis town,

Ganzhou District of Zhangye City, as a research case. From the perspective of the landscape and land

use/cover, we use the boundary of the central city of Ganzhou District in 1987 as the starting boundary of

radiation, and divide the radiation area into 15 radiation rings to analysis the spatial expansion and radiation

effects of oasis towns, the results show that the land use/cover change rate changes little before the new

century and changes dramatically after the new century. Among the responses, the construction land and

cultivated land are the strongest. The ring structure of the oasis radiation effect is obvious, which shows that

1 to 5 km is the radiation core zone(core ring layer) of the town, 6 to 10 km is the radiation transition

zone(transition ring layer), and 11 to 15 km is the periphery zone (periphery ring layer). A land use transfer

matrix shows that the land use conversion is more intense in the core ring layer, the main cause is cultivated

land and grassland are transform into construction land, while in the periphery layer, the conversion ratios

of other land types and construction land have a higher proportion, indicating that the expansion of towns is

constantly expands to the periphery.

1 INTRODUCTION

Urban expansion is one of the most obvious spatial

features of urbanization, and which is also an

important measure of urbanization, so urban

expansion is one of the focus issues of human

geography. From the perspective of land use change,

the urbanization process means the process of spatial

expansion of construction land, and the expansion of

construction land will result in the reduction of

cultivated land. Therefore, land use/cover change

(LUCC) in the process of urbanization has also

become one of the focus issues of geography and

ecology (Qiao et al., 2013). Most of the urban

expansion studies are concentrated in developed

regions (Xu et al., 2012;Pei et al., 2015), and there

are relatively few studies focus on underdeveloped

regions. Compared with the spatial expansion of

inland cities, the spatial expansion of oasis towns is

constrained by water resources, so the impact on the

change of land use types is greater to the

surrounding areas and the radiation distance is much

further (Fang et al., 2007). Regarding the oasis

towns research, most of which study from the

perspective of the urban systems (Qiang et al., 2010)

and urban development model (Ma et al., 2006), and

less perspective is from the landscape, bases on the

spatial expansion of oasis towns (Zhang et al., 2010).

Urban spatial radiation effect mainly refers to the

increase of construction land, results in a regular

change of land use/cover type in the adjacent area

within the urban radiation area. The research

methods of urban expansion include: Expansion

speed and Expand Intensity Index (EII), Space

Syntax Expand Intensity Index (SS-EII), Center of

gravity coordinates, Location entropy (Li et al.,

2017;Wang et al., 2016), and so on. Alimujiang

studied the spatial-temporal dynamic changes of the

Xinjiang Oasis by means of remote sensing and GIS,

which indicate that the urban spatial structure of

Oasis tends to be much more loosen (Alimujiang et

al., 2013); Yu carried out multi-objective

Zhang, X. and Luo, J.

Study on the Radiation Effect of Urban Spatial Expansion in an Oasis - A Case Study of Ganzhou District in Zhangye City.

In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 207-213

ISBN: 978-989-758-342-1

207

optimization of land use status in Kuitun, Xinjiang

(Yu et al., 2013), which has laid a foundation for the

study of land use and spatial expansion of oasis

cities. Based on the related research (Zhang et al.,

2010;Liang et al., 2011;Wu et al., 2012;Ma et al.,

2017;Liu et al., 2015), we take Ganzhou District of

Zhangye City, Gansu province as a case area, from

the perspective of spatial expansion of construction

land, adopt the ring layer method, land use dynamic

degree and land use transfer matrix to analysis the

radiation effects of urban expansion, and define

urban expansion throughout the changes of land use

landscape.

2 OVERVIEW OF THE STUDY

AREA

The Ganzhou District of Zhangye City is located in

the middle of Hexi Corridor. The longitude is

between 100°04'~100°52', and the latitude is

between 38°32'~39°24', which is east of and

adjacent to Shandan and Minle county, south to

Yugu Autonomous County, west to Linze County,

and north to the Alashan Right Banner of Inner

Mongolia Autonomous Region. The district

administers a national-level economic and

technological development zone, 18 townships, five

sub-district offices, and 245 administrative villages.

The area is 65 km long from east to west, 98 km

wide from north to south, and has a total area of

3657 km

. The Zhangye Oasis, which is the largest

oasis in the Hexi Corridor of China is in the process

of development. The scale, social, and economic

development of the oasis is faced with great

ecological and environmental problems, which made

this area a representative area within the oasis.

3 RESEARCH METHODS

3.1 Data Sources and Processing

The remote sensing data uses in the study is sourced

from Landsat TM satellite is provided by the United

States USGS website and the Chinese Academy of

Sciences Computer Network Information Center

geospatial data cloud, and which includes the data of

1987, 1995, 2000, 2006 and 2011. Based on the

landscape classification system, interpretation is

completed through visual analysis. Then, we correct

the data by using land use maps, Google Earth high-

resolution images, and field survey results at

different periods in the region, and finally the

acquisition of land use data for different periods in

Ganzhou District. Through the examination of the

interpreted results, the overall accuracy is over 90%,

which satisfies the precision requirements of the

research. The land use classification refers to the

Classification of Land Use Status (GB/T21010-2007)

and the classification for land use/coverage

classification system of the national remote sensing

monitoring. Combined with the landscape

characteristics of the study area, the research area is

divided into six landscape types: cultivated land,

forest land, grassland, construction land, water area

and unused land, where construction land includes

urban land, rural residential land and other

construction land. Figure 1 shows the land use in

1987.

Figure 1: Map of the Ganzhou District center land-use in

1987 and the division of the radiation ring layer.

3.2 Sample of Radiation Scale

The spatial extent of the radiation range is related to

the economic development level of the city. Some

relevant scholars use the market breakpoints to study

the economic radiation range in developed cities,

and conclude that the radiation range is from 30 to

200 km. For this research studies from the

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208

perspective of land use, and Ganzhou District is an

underdeveloped region, so the scope of the

expansion of construction land is determined to be

15 km. Taking the boundary of the central city of

Ganzhou District in 1987 as the starting boundary of

radiation and the interval of 1 km as the radiation

impact analysis scale, then used ArcGIS 9.3 to make

multi-ring buffer for all the 5 phases data, and

finally format the 15 spatial scales. Fig.1 shows the

division of the radiation ring layer.

3.3 Spatial Radiation Effect

Measurement Methods

3.3.1 Analysis of Land Use Dynamic Degree

Analysis on dynamic degree of land use: Using the

dynamic model, including single and comprehensive

land use dynamic degree, to analyze the land use

changing trend. The single land use dynamic degree

formula is as Eq.1.

%100







(1)

Where K means the dynamic degree of one type

of land use in the study area; U

are determined

separately for the number of land use types in the

beginning and end of the study period; T means the

study period, if T represents year, then K value is the

annual rate of one land use type in study the region.

3.3.2 Land Use Transfer Matrix.

The land use transfer matrix is used to calculate

different types of area transfer rates(T

), and then to

analyze the mutual transformation between land use

types in different radiation ranges. The transfer rate

are calculated as follows:

ij ij ij

100

TA A







(2)

refers to the proportion of land use/cover type

i in the k period is converted to land use/cover types

j in the k+1 period; A

refers to the land use area.

With the continuous outward expansion of the

urbanized ring, the area of the radiation zone is

getting larger and larger. To make the analysis data

comparable, this paper uses relative area (a ratio of

land use/coverage type area to radiation circle area)

to analysis the radiation effect.

4 RESULTS ANALYSIS

4.1 Analysis of Land Use Dynamics

Figure 2 shows the dynamic degree of landscape

types varies with the radiation distance at different

times. The dynamic degrees of construction land in

different stages are all positive; indicating that the

construction land area is increasing continuously,

the time period of the maximum dynamic degree is

from 2006 to 2011, which is in the 3

ring. The

minimal dynamic degree is from 1987 to 1995, all

the change rate are less than 5%. The dynamic

degrees of cultivated land are not all positive; the

negative values converted into positive values are in

the 4

and 5

ring in each study period, from 2006

to 2011, the change rate is the largest and in the 1

ring the cultivated land has the fastest reduction rate.

Grassland changes show two obvious changes stages.

First, the dynamic degree in the 5

ring reached the

positive maximum from 2006 to 2011, and the other

is that the dynamics of the 8

to 12

ring alternated

between positively and negatively. The change trend

of forest land is relatively simple, within the 2

the 7

rings, which remains unchanged. Within the

to the 11

rings, there is a slight increase and

decrease in small fluctuations, the change in the 14

ring is more obvious. The dynamic degree of the

water area fluctuates greatly in the first six rings,

and from the 7

ring, the dynamics of each period

are negative. The dynamic degree of unused land is

basically negative, and the absolute value of

negative value increases with time, indicating that

the reduction of unused land is more distinctly.

4.2 Analysis of Time-Space Scale Effect

Figure 3 shows the distinctive features of each ring

in Ganzhou District. In terms of time, within the 5

ring, the proportion of cultivated land is the largest,

the advantages of other landscape types have

gradually decreased with the passage of time, and

the cultivated land area decreased the fastest and

greatest, but the proportion of construction land has

become ever larger. Beyond the 10

ring of the oasis,

the proportion of cultivated land increases year by

year, and the area of unused land continues to

decrease.

Study on the Radiation Effect of Urban Spatial Expansion in an Oasis - A Case Study of Ganzhou District in Zhangye City

209

Figure 2: Dynamic degrees of different landscape types in different radiation ranges from 1987 to 2011.

Figure 3: Changes in landscape types with different radiation ranges from 1987 to 2011.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

change rate

（%）

radiation range

（a）construction land

-10

-5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

change rate

（%）

radiation range

（b）cultivated land

-14

123456789101112131415

change rate

（%）

radiation range

（c）grassland

-50

100

2 3 4 5 6 7 8 9 10 11 12 13 14 15

change rate

（%）

radiation range

（d）forest land

-14

-4

123456789101112131415

change rate

（%）

radiation range

（e）water area

-20

-10

123456789101112131415

change rate

（%）

radiation range

（f）unused land

1987 to 1995

1995 to 2000

2000 to 2006

2006 to 2011

50%

100%

123456789101112131415

Relative area

percentage

radiation range

1987

50%

100%

123456789101112131415

Relative area

percentage

radiation range

1995

50%

100%

123456789101112131415

Relative area

percentage

radiation range

2000

50%

100%

123456789101112131415

Relative area

percentage

radiation range

2006

100%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Relative area

percentage

radiation range

2011

grassland

cultivated land

construction land

forest land

water area

unused land

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210

Spatially, we can see the dominate landscape in

different rings are different. Cultivated land is the

largest proportion of all landscape types, and it is

consistent with the main industry of agriculture in

Ganzhou District, which demonstrates that the

cultivated land is the substrate of the oasis. When

moving outward, the dominant position of cultivated

land is gradually weakened. The construction land is

mainly concentrated within the 5

ring, and beyond

this ring the advantage gradually decreases. Forest

lands and grasslands are concentrated mainly in the

oasis periphery or areas outside the 9

ring, and the

proportion of waters area in each ring is relatively

low. As the ring numbers increase outward, the ratio

of unused land area has gradually increased, and

undeveloped land begins dominate in the 15

ring.

Generally, as we progress from the inside ring to the

outside ring, the landscape characteristics present as

“construction land, cultivated land, and unused

land”.

4.3 Land Use Transfer

In order to highlight the typicality and

representativeness, this paper chooses the 1

, 4

, 9

and 15

rings of land circulation to analysis the land

use transfer situation from 2006 to 2011.

The results in Table 1 implies that the conversion

ratio of construction land in each ring is 100%, and

the conversion of land in the 1

ring only occurs into

the grassland, farmland, water area and construction

land categories. The highest proportion which is

converted into construction land is grassland,

followed by cultivated land, and the proportion is 50%

and 34.6%, respectively.

Table 1: Land Use Conversion Matrix from 2006 to 2011 (Unit: %).

Radiation

rings

2006

2011 grassland cultivated land

construction

land

forest land

water

area

unused

land

ring

grassland 46.5 1.5 75.7

cultivated land 3.5 63.8 23.9

construction land 50.0 34.6 100 0.4

water area 0.1

ring

grassland 72.8

cultivated land 0.3 95.8 5.7 0.9

construction land 15.5 3.8 100 10.19 5.7 54.3

forest land 11.4 89.81

water area 0.4 88.4 13.3

unused land 0.2 31.5

ring

grassland 62.9 6.4 2.4

cultivated land 19.5 98.8 6.2 64.4 13.5

construction land 0.7 100 2.0

forest land 17.6 0.4 87.4 2.5 12.0

water area 0.1 28.7 2.6

unused land 4.4 67.5

ring

grassland 82.0 0.4 46.9 2.2

cultivated land 14.0 98.5 43.7 12.4 5.7

construction land 3.6 1.0 100 0.1

forest land 0.0 0.0 9.4 0.6

water area 0.0 0.0 82.5 0.5

unused land 0.4 0.1 5.1 90.9

Study on the Radiation Effect of Urban Spatial Expansion in an Oasis - A Case Study of Ganzhou District in Zhangye City

211

In the 4

ring, all types of land have been

converted into construction land, of which the

highest conversion ratio is unused land, followed by

grassland and forest land. In the 9

ring, the main

land converted into construction land wasunused

land and cultivated land, but the proportion was

small. In the 15

ring, in addition to self-

transformation, there is a small part of grassland,

cultivated land, and unused land converted into

construction land.

The proportion of grassland converted to

construction land in the 1

ring is much higher, and

the ratio of conversion to forest land is increased in

the 4

ring. In the 9

ring, the grassland is converted

to cultivate land and forest land. In the 15

ring,

grassland is mainly converted to cultivated land.

Cultivated land in the 1

ring is more intense, and

other rings are less transferred, indicating that the

protection of cultivated land is conducive to stabilize

the amount of cultivated land. The conversion of

forest lands in the 1

, 4

and 9

rings is relatively

small, but in the 15

ring, the conversion ratio to

farmland and grassland significantly increases. The

conversion of water area is closely related to

cultivated land. Unused land is mainly converted to

construction land in the 4th ring, and is converted to

cultivated land and forest land in the 9

ring.

Generally, with the passage of time, land use

conversion is more and more frequently, especially

the increase of the conversion intensity of unused

land, indicating that the utilization rate of unused

land is getting higher and higher. Although

cultivated land was occupied to a certain extent

during the study period, which occurs in the core

area of the town, and the conversion ratio of

cultivated land in other rings is not significant,

indicating that the cultivated land is well protected

during the expansion of the oasis towns in Ganzhou

District.

5 CONCLUSIONS AND

DISCUSSION

In the process of development, oasis cities and

towns are constrained by various factors, such as

water resources, desertification, land use patterns,

and land management levels. This paper mainly

analyzes the land use/cover change and radiation

effect of the oasis towns from the point view of land

landscape, which shows that the effect of the ring

structure of urban radiation becomes more and more

obvious with the passage of the time. The main

conclusions are:

(1) The dynamic changes of land use in oasis

towns show that in the time series, from 1987 to

1995, the change rates of all the land use types are

the lowest, while the highest change rate is in the

phase of 2006 and 2011. The change of land use

cover in different time periods is different in

different rings, and the change rate of construction

land in different radiation distances is greater than

zero, indicating that the area of construction land is

continuously increasing. The change rate of

cultivated land is negative within the 5

ring, and

positive from the 5

ring, showing that the closer the

distance from the core area is, the faster the

cultivated land area decreases.

(2) By calculating the relative area ratio of each

ring, three different radiation ring layers can be

concluded: 1 to 5 km is the radiation core zone of

the town; 6 to 10 km is the radiation transition zone

of the town, while 11 to 15 km is the periphery zone

of the town. As the radiation area continues to

expand, the area ratio of construction land gradually

decreases. In the core zone, the increase of

construction land and the decrease of cultivated land

maintain the opposite trend, indicating that the

expansion mode of the urban core area of Ganzhou

Oasis has taken up amount of cultivated land.

(3) The land use conversion is more intense in

the core ring layer, and not obvious in the outer ring

layer. The main conversion sources of the

construction land are from the core zone, which are

cultivated land and grassland. Land use conversion

is characterized by the disappearance of unused land

in the 1

ring, which translates into construction

land, and from other side, it greatly improves land

use efficiency. In the outer ring, the proportion of

other types of land converts into cultivated land

increases, and urban expands to the periphery. The

grassland conversion mainly takes place in the 1

and 4

rings, and is mainly converted into cultivated

land and construction land; the cultivated land

conversion mainly takes place in the 1

ring, which

is mainly transformed into construction land; the

transformation rate of forest land, water areas and

unused land in each ring has increased, but not

obvious.

The spatial radiation effect of urban expansion is

due to the increase of land use in cities and towns,

resulting in a corresponding spatial pattern of

changes in other types of land use. Urban expansion

is influenced by many factors such as natural

IWEG 2018 - International Workshop on Environment and Geoscience

212

geography, government decision-making, urban

planning, economic factors, and transportation,

compared with other regions, the oasis region is

constrained by water and land resources, and the

urbanization process has a greater impact on the

transformation of land use types in the surrounding

areas. On the spatial scale, the core area of oasis

towns has obvious influence on the land use change

in adjacent areas, among which the changes of

cultivated land, grassland, construction land and

unused land all have certain regularities. Far from

the central city and town, cultivated land and

grassland decrease first and increase later.

Construction land gradually decreased with the

distance far from the town centre, while the unused

land was in the opposite. The results of the study

may be affected by the distance of the radiation

circles, different scales will lead to different

conclusions. Future research will focus on the

selection of the radiation circle and scale study, and

how the different scales effect on land use change.

ACKNOWLEDGEMENTS

This work is funded by National Natural Science

Foundation of China (Grant No. 41661035) and

Young Teachers Scientific Research Ability

Promotion Plan of Northwest Normal University

(Grant No. NWNU-LKQN-14-14).

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