FuhaiWANG，Qigang ZHOU，Fei YANG，Pengwu YANG ，Yao WANG

1.School of Tourism and Land Resources，Chongqing Technology and Business University，Chongqing 400067，China；2.Research Centre of the Economy of the Upper Reaches of Yangtze River，Chongqing Technology and Business University，Chongqing 400067，China

Land is the fundamental element for human survival and development，and also means of production and source of agriculture and industry.The human-land conflict is outstanding in the Three gorges Reservoir Region.Reasonable use of land directly relates to improvement of residents'living conditions，economic construction，and ecological protection of the Three-gorges Reservoir Region.Analysis of current land use situation is the process of evaluation and study on land use type，quantity，and distribution and combination characteristics，and the analysis results can reflect characteristics，weakness and strength of land in the Three-gorges Reservoir Region，which is helpful for diagnosing whether land use is proper［1］.Selecting the Three-gorges Reservoir Region as the study region has following considerations.Firstly，it is expected to find out characteristics and trend of land use changes in the Three-gorges Reservoir Region，to provide guidance for land use planning.Secondly，it is intended to reflect functions of social and economic indicators to land use changes from the perspective of quantitative analysis.Besides，it is expected to enrich studies on land use changes and verify applicability of traditional study methods.In this study，with the aid of theories of geographimetrics and landscape ecology，we made an overall analysis on current land use situations in the Three-gorges Reservoir Region，in the hope of providing basis for optimization and adjustment of land use structure.

1 Overview of the study area

The Three-gorges Reservoir Region（106°16′E-111°28′E，28°56′N-31°44′N）is located in the upstream of the Yangtze River at the boundary of Chongqing Municipality and Hubei Province with the area of 57 336 km2and with the population of 34.509 7 million in the end of2010（including23.173 6million agricultural population，accounting for 67.15%）.It stretches along the Yangtze River from Jiangjin District of Chongqing to Yiling District in Yichang City of Hubei，which is very narrow and where the geography is complex.The permanent resident population of the Three gorges Reservoir Region is30.324 96million.The urbanization rate reached from 28.42%in 2009 to 32.85%in 2010.Per capita GDP of the Three-gorges Reservoir Region was 23 796.2 yuan in 2010.

2 Data source and data processing

In this study，we used Landsat TM images as data source.The ground resolution of TM is30m.In the whole Three-gorges Reservoir Region，it involves 9 images with orbit number 125038，125039，126038，126039，127038，127039，127040，128039，and 128040 respectively.Since original images have such problems as geometric distortion，indistinct spectral characteristics，and separation of several wave bands，it is necessary to take technical processing of original images，such as geometric correction，image enhancement，and image fusion［2-3］.After a series of processing，we carried out artificial visual interpretation of remote sensing images and obtained vector data of current land use situation of the Three-gorges Reservoir Region in 2010.

3 Analysis on structure of current land use

With the aid of GISs of t ware，we analyzed interpreted data of cur-rent land use and the results are listed in Table 1.The whole Three-gorges Reservoir Region covers an area of 57 336 km2，including 28 987.95km2forest land（accounting for 50.56%），22 554.3 km2cultivated land（accounting for 39.34%），3 184.43 km2grassland（accounting for 5.55%），1 293.97 km2waters（accounting for 2.26%），286.89 km2construction land（accounting for 2.24%），and 28.46 km2unused land（accounting for 0.05%）.

Table 1 Land use situation of districts or counties in the Three-gorges Reservoir Region in 2010

4 Analysis on quantity structure of current land use

The analysis on quantity structure of land use is to study diversity，combination type and location significance of quantity combination of various land types，so as to analyze the difference in current land use.

4.1 Diversity analysisThe diversity index of land quantity structure is used to characterize completeness of various land types，and the major analysis method is Gibbs-Mirtin index（GM）model［4］.The mathematical formula of this model is as follows：

where fidenotes total area of the i-th land use type.

From Formula（1），GM value is0-1；when GM∝1，it indicates that centralization degree of land use is high；otherwise，when GM∝0，it indicates low degree of centralization.If the type is rich and land area of different types is balanced，GM∝1；if the land use type is single，GM∝0.Therefore，GM model can reflect the completeness of land use types.

Using the data in Table 1，we can calculate the diversity index of current land use situation of the Three-gorges Reservoir Region and 26 districts or counties（as listed in Table 2）.Analysis results show that the overall land use diversity index of the Threegorges Reservoir Region is0.59 and the land use type is relatively rich.Jiangbei，Dadukou，Shapingba and Nan'an District have the highest diversity index，respectively 0.7，0.69，0.66 and 0.66；Yubei，Zhongxian，Jiangjin，Zigui，Ba'nan，Shizhu，Wushan，Fengjie，Changshou，Wuxi，Yuzhong and Xingshan have lower diversity index.Xingshan County has the lowest diversity index of land use（0.32），indicating that its land use type is single.

Table 2 Land use diversity index of Three-gorges Reservoir Region and districts or counties

4.2 Analysis on combination typesIn recent years，Weaver-Tomas combinationmodel is deemed as the bestmethod for solving land structure problem.Itsbasic principle is to compare actual distribution and assumed uniform distribution of land use types one by one，to find outone uniform distribution closest to the actual distribution，and the combination type of such distribution is the desired combination type［5］.

Firstly，rank land use types from high to low area of percentage.Secondly，assume land is allocated to one type，two types，etc.When the land is allocated to the first type，the distribution is 100%，and the distribution of other types is 0；when the land is allocated to the first two types，the distribution is50%respectively，and the distribution of other types is0，and so on and so forth，till land is evenly allocated to all types.Next，calculate the combination coefficient through square sum of difference of corresponding items according to each type of assumed distribution and actual distribution.Finally，the assumed distribution corresponding to minimum combination coefficient is the land use combination type of the corresponding region.According to the above principle，we can obtain land use combination types of the Reservoir Region and districts and regions，as listed in Table3.From Table 3，we can see that there are two land use combination types in the Three-gorges Reservoir Region，i.e.＂forest land-cultivated land＂combination type.As to single districtor county，Dadukou，Shapingba，Nan'an and Jiangbei have three combination types，other districts or counties have one or two combination types，showing that most districts or counties have weak overall land use function，especially，Yuzhong，Wuxi，Xingshan and Yiling have single land use function.

4.3 Analysis of location indexThe location is specific manifestation of organic combination of natural geographical position，economic geographical position，and traffic geographical position in space.Through analysis on the location index of land use，it is able to reflect relative centralization of various land use types of a region at a higher level of regional space.The calculation formula for specific location index（Qi）［4］is as follows：

where fiis the total area of the i-th land use type；Fiis the total area of corresponding land use type in higher level region；Σfiis the sum of land area in this region；ΣFiis the sum of land area in higher level region.If Qi＞1，it indicates that the location significance of land use type is relatively obvious；the higher the Qi，the greater significant it is.

From Table 4，cultivated land has location significance in most districts and counties.Thus，cultivated land is the major land use type in the Three-gorges Reservoir Region.In Yuzhong District，the construction land has the highest location index（34.5922），showing Yuzhong District has the highest degree of land construction and use；in Fengjie，Wuxiand 4 districts（counties）of Hubei Province，forest land has location significance，indicating that these areas are rich in forest resources；in Yubei，Fuling，Wulong，Fengdu，Shizhu，Zhongxian，Wanzhou，Kaixian，Yunyang and Wuxi，the grassland has location index greater than 1，showing obvious grassland advantage.

4.4 Analysis on land use degreeLand use degree mainly reflects influence degree of human factors in land system，while land system is a natural and social complex.The land use degree can be graded as follows：agricultural land，forest land and grassland，urban community land，and unused land levels.The land use grading index of cultivated land is1；the land use grading index of forest land，waters and grassland is2；the land use grading index of construction land is 3；the land use grading index of unused land is4；the composite index of land use degree（La）can be expressed by following formula［6］：

where Aiis the grading index of land use degree of a certain land use type in a region；Ciis the area percentage of this land use type.From formula（3），it is known that the composite index of land use degree is a continuous function with value in the range of［100，400］.In certain unit of network region，the value of com-posite index reflects degree of land use.The land use degree of any region can be obtained through calculating its composite index.Since driving factor of land use changes comes from nature and society，using the composite index of land use degree can better manifest the influence of natural and social factors on land use.

Table 3 Combination types of land use in districts or counties of the Three-gorges Reservoir Region in 2010

Table 4 Location index of land use in districts or counties of the Three-gorges Reservoir Region in 2010

Continued Table4

Table 5 Composite index of land use degree of the Three-gorges Reservoir Region and districts or counties

Table 5 indicates that Yuzhong District has the highest land use degree，and Changshou District is lowest in land use degree；the land use degree of Dadukou，Xingshan，Yiling，Shapingba，Jiangbei，and Wuxi is about equal and relatively high；the land use degree of Yunyang， Wuling， Beibei， Fengdu， Fuling，Jiangjin，Wanzhou，Yubei，Kaixian，Ba'nan，Zhongxian and Changshou is lower than the average level of entire reservoir region.

5 Conclusions

In the entire Three-gorges Reservoir Region，forest land takesup a half，in some districts and counties，forest land coversmore than 80%，indicating that the Reservoir Region hasmuchmountain area and the forest resource is rich.There are significant differences in land use in districts and counties of the Three-gorges Reservoir Region.Land types diversity，combination types and location index are also varied.In Yuzhong District，except waters，other land use types aremainly construction land and the land use type is single；as to the diversity index，Xingshan County has the largest single land use type，mainly forest land.As to land use degree，Yuzhong District has the highest degree of land use，while Changshou District has the lowest composite index of land use.

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