On the basis of CLUD from 2000 and 2010 (Liu et al., 2010; Kuang et al., 2013; Zhang et al., 2012), we updated the land use datasets in 2013 by human-computer interactive method. This method specifically identified the land use changing objectives by comparing the remote sensing images for two periods in 2010 and 2013. We updated a national land use database with a scale of 1:100,000. Then we developed the database of built-up area for the two periods 2000-2010 and 2010-2013. High resolution remote sensing image covered the whole country were used to update CLUD. Although data from Landsat TM did not cover the whole of China or was of poor quality for some regions, data was used from the Resources satellite third (ZY3) and the high precise image from the Google Earth to supplement it, and better data from different sensor types and time phases was selected as appropriate to improve interpretation and mapping accuracy. The vector datasets were applied to extract and calculate the area of each type of land including cultivated land, woodland, grassland, water body, urban and industrial land, and unused land and their 25 sub-class from CLUD classification system. To ensure the quality and accuracy of data, a nationwide field survey was carried out during the preliminary interpretation of the 2013 data, and samples equivalent to 10% of all counties were randomly selected for the field survey data and field records for the sake of verifying accuracy. The accuracy of first-level land categories was higher than 94.3% and that of sub-class was higher than 91.2%, which was enough for 1:100,000 scale mapping accuracy.

In addition, the study further divided built-up area into three second-level land use categories, namely urban land, rural residential land, and factory, mine and transportation land. Urban land refers to built-up areas of land in large, medium-sized and small cities and towns. Rural residential land refers to land of residential areas smaller than towns. Factory, mine and transportation land refers to land occupied by factories, mines, large industry, oilfields and quarries, or special sites such as airports and ports.

The data on Major Function-oriented Zones used in this study mainly came from the National Plan for Major Function-oriented Zones issued by the State Council and the Scheme for Major Function-oriented Zoning in China (V1.0) (Fan, 2015). Major Function-Oriented Zones were divided into optimal development zones, key development zones, restricted development zones and prohibited development zones according to their development methods, and restricted development zones were further divided into agricultural production zones and key ecological function zones. Optimal development zones, such as the Bohai Rim, the Yangtze River Delta and Pearl River Delta regions, are relatively strong overall, have large-scale economies, relatively sound systems of urban and rural construction, relatively strong internal economic ties and a strong scientific foundation for innovation. Key development zones, such as the middle reaches of the Yangtze River, central and southern Hebei and Central Plains economic zone, are regions that usually have strong economic foundations, the beginnings of systems for urban development and can promote development in surrounding areas. Restricted development zones are agricultural production zones and key ecological function zones where large-scale and intensive urban construction are restricted. Prohibited development zones are areas of strict ecological protection where industrialization and urbanization are prohibited (Fan, 2015). Since prohibited development zones are function-oriented zones superimposed on the former three types of function-oriented zones, and there is relatively few of them compared to the other types, this study chose not to deal with them. MFOZs are also designated as national-level or provincial-level zones based on the regional function hierarchy, and this paper focuses on national-level Major Function-oriented Zones, with no consideration given to provincial-level zones. The Draft of Major Function-oriented Zoning in China (V1.0) primarily dealt with provincial administrative zones. But attempts to coordinate with other indicators and plans meant that some zones had two or more zoning classifications. Where this study has dealt with provincial administrative zones, zones that contain two or more types of major functions have been removed, leaving only those counties that have one type of major function (Figure 1 and Table 1).

In order to better reveal the characteristics and regional differences between each major function-oriented zone, this study divided China into four major zones (eastern, central, western and northeastern regions - see Figure 2 and Table 2) based on economic and social development factors. As the majority of optimal development zones are located along the coast, during the discussion of optimal development zones we have subdivided them into those in the Beijing-Tianjin-Hebei region, the Yangtze River Delta, the Pearl River Delta, central and southern Liaoning, and the Shandong Peninsula.

In order to better show the speed and intensity of development of built-up area, this study used the indicators “built-up area expansion rate” and “dynamic degree of built-up area expansion”, both of which are stated as a percentage per year (%/yr). The formula for calculating the built-up area expansion rate is as follows:

$K=\left\{ \sum\limits_{ij}^{n}{\left( \Delta {{S}_{ij}}/{{S}_{i}} \right)} \right\}\times \left( 1/t \right)\times 100%$ (1)

where S_i is the area at the start of monitoring built-up area, ΔS_ij is the total area of changed land type from and to built-up area during the monitored period, and t is time. The rate of change of built-up area, K, therefore reflects the built-up area expansion rate within the study area during the certain period.

The formula for calculating the dynamic degree of built-up area expansion is as follows:

$S=\left\{ \sum\limits_{ij}^{n}{\left( \Delta {{S}_{i-j}}/{{S}_{a}} \right)} \right\}\times \left( 1/t \right)\times 100%$ (2)

where S_a is the study area, ΔS_i-j is the total area of changed land type from and to built-up area during the monitored period, and t is time. S is the dynamic degree of built-up area expansion, which reflects the intensity of change from others to built-up area within the study area during the certain period.

The total area of built-up area in national Major Function-oriented Zones was 17.22×10⁴ km² in 2013, accounted for 1.79% of China’s land area. Of this, optimal development zones, key development zones, agricultural production zones and key ecological function zones accounted for 3.74×10⁴ km², 4.25×10⁴ km², 7.61×10⁴ km² and 1.63×10⁴ km², respectively, or 27.02%, 6.27%, 4.18% and 0.43%, respectively, of the total land area within each of their function-oriented zones (Table 3). It is therefore possible to see the gradient feature of land development in different MFOZs. The area proportion of built-up area sub-class in different Major Function-oriented Zones is clearly different. The amount of urban land in optimal development zones has reached 50.82%, which reflects the urban-centered development model in those regions. The area proportion of urban land, rural residential land and land for factories, mines and transportation in key development zones was 36.4%, 44.41% and 19.19%, respectively, which reflected the equal condition on urban, rural and industrial development in key development zones. Rural residential areas accounted for 71.03% of agricultural production zones and 68.01% of key ecological function zones, which reflect the fact that the focus of these two types of zones is on rural development (Table 4). Thus, the area proportion of built-up area sub-class clearly reflected the different development stages of the MFOZs.

In 2013, built-up area of optimal development zones was mainly located in Beijing and Tianjin of the Beijing-Tianjin-Hebei region, the Yangtze River Delta and the Pearl River Delta, and crossing area across central and southern Liaoning and the Shandong Peninsula. Built-up area of key development zones was mainly located in eastern coastal regions, Tianjin Binhai New Area, southern Hebei, the border region between Shandong and Jiangsu, central Shanxi, northern Henan and eastern Hubei, with relative concentrations in central Sichuan, central Shaanxi and Chongqing. Built-up area of agricultural production zones was mainly located in eastern coastal region, including large parts of Hebei, Shandong and Jiangsu, central region including large parts of Henan and Anhui, as well as western parts of the northeastern region. Built-up area of key ecological function zones was relatively dispersed and scattered across the country (Figure 3).

The national expansion in built-up area in the period 2000-2010 mostly took place in the eastern coastal and central regions, with fast expansion also occurring in southern areas of China’s northeast and southern Gansu, eastern Sichuan and Chongqing in the west. Of these, areas with the most obvious increases in built-up area were located in Beijing and Tianjin, the Yangtze River Delta, the Pearl River Delta, Chongqing and Chengdu, with relatively increases in built-up area also occurring around provincial capitals in the central region (Figure 4a). Areas with the most notable increases in built-up area during the period 2010-2013 were mainly located in the Yangtze River Delta, followed by the Bohai Sea region, with insignificant increases in most of the northeastern regions (Figure 4b).

Compared to the period 2000-2010, the area of built-up area in four Major Function- oriented Zones increased to varying degrees (Figure 5b) in the period 2010-2013. The largest increase for 2000-2010, 986.32 km²/yr, took place in optimal development zones, whereas the same zones registered much slower growth in the period 2010-2013, with key development zones having the largest increase of 1746.27 km²/yr (Table 4). Compared to the former 10-year period, the latter three years saw a significant decrease in the growth rate of built-up area in optimal development zones, but a significant increase in the growth rate in other MFOZs (Figure 5c). Key development zones, for example, experienced a rate of change of 4.68%/yr, while the rate of change in key ecological function zones was 2.79 times faster for 2010-2013 compared with 2000-2010, though their average area of expansion remained the lowest (see Table 4). Moreover, during the last three years of the study period, the dynamic degree of each type of major function-oriented zone improved. Optimal development zones had the lowest increase, while key ecological function zones had the highest (Figure 5d). However, during the period 2010-2013, optimal development zones had the most dynamic built-up area, with a value of 0.79%/yr, and although dynamic degree was basically the same as the previous 10 years, they were still more dynamic than the three other types of Major Function-oriented Zones (Table 4).

During the periods from 2000 to 2010 and from 2010 to 2013, the areas of built-up area in four Major Function-oriented Zones all increased. The increased total area of built-up area from 2000 to 2010 is larger than the total increased area of built-up area from 2010 to 2013. But the annual area and annual rate of increased built-up area are of great difference between the four MFOZs. In the optimal development zones, the annual increased area of built-up area in 2010-2013 is almost the same with the one in 2000-2010, only with a little increase. And the annual increase rate decreased slightly. The expansion of built-up area in optimal development zones is mainly from the expansion of the large and medium scale cities. The increased area of built-up area is mainly from the encroachment of urban built-up area in the farmland around the city and suburbs. In the optimal development zones, which are the eastern coastal and the northeastern regions, the expansion shows a “slow down in the south, keep flat in the north, and speed up in the central part” spatial pattern. Compared to the previous decade, the annual change area and annual change rate of built-up area in the key development zones increased a lot in 2010-2013, almost twice the previous decade. The increase of built-up area is mainly from the sprawling of the rural and urban land. On the national scale, the expansion of built-up area in the key development zones shows a trend of “sharp acceleration in the western and northeastern, keep essentially slowing growth in the central and eastern coastal regions”. Compared with the previous decade, the annual change area and rate of built-up area in agricultural production zones increased significantly in 2010-2013. The annual change area has increased by 1.5 times while the annual change rate has increased by 1.3 times. The expansion of built-up area in the agricultural production zones shows a trend of “significant growth in the whole region, abrupt acceleration in the western”. In the key ecological function zones, compared to the 2000-2010, the annual change area of the built-up area increased by about 2 folds and the annual change rate increased by about 1.8 times during the period 2010-2013. The expansion of built-up area in the key ecological function zones shows a trend of “significant growth in the whole region, abrupt acceleration in the western part, and slowdown in the northeastern part”. Both in the agricultural production zones and key ecological function zones, the increase of built-up area include the expansion of both urban land and rural settlements. But because of the high proportion of the rural residential area, the expansion of built-up area is mainly because of the expansion of the rural residential land.

Overall, since the plan for Major Function-oriented Zones was promulgated, the rate of expansion of built-up area in optimal development zones has been effectively controlled and the annual rate of change has decreased significantly. However, because of a smaller total area, with a relatively large scope of built-up area to develop, the optimal development zones would remain most dynamic during the latter three-year study period. This shows that to some extent, since the implementation of the Major Function-oriented Zones plan, the urbanization process in optimal development zones has been transformed from a simple expansion of the urban land to the optimization of urban structure which is an optimum development direction. However, the annual rate of change and dynamic degree of built-up area in key development zones, agricultural production zones and key ecological function zones during the period 2010-2013 increased greatly. The high rate of and intense expansion of built-up area in key development zones shows that the urbanization in key development zones is speeding up. This is the most direct show of the performance of the Major Function-oriented Zones plan in the key development zones. Although the rate of change and dynamic degree of built-up area in agricultural production zones and key ecological function zones was still quite low in the last three years of the study, compared with the first 10 years of the 21st century, the growth rate was still excessive and not in line with the level required for “restricted development” in the MFOZ plan.

There was fast expansion of built-up area in optimal development zones during the period 2000-2010, particularly in the Yangtze River Delta and Pearl River Delta regions, as well as in Beijing, Tianjin and Shenyang. Built-up area expansion in the 10 km × 10 km grids exceeded 10% on average, and in some cities with rapid economic growth, such as Guangzhou, Shenzhen, Beijing, Tianjin, Shanghai, Suzhou and Wuxi, expansion of built-up area in each 10 km × 10 km grid exceeded 20% (see Figure 6a). Compared to the previous decade, the speed of expansion of built-up area in many optimal development zones decreased, most noticeably in the Pearl River Delta, while Beijing, Tianjin and their surrounding areas experienced only small increases, and built-up area in the Yangtze River Delta region continued to increase significantly in the three years after the plan for Major Function-oriented Zones was promulgated (Figure 6b).

In terms of the amount, the annual area change of built-up area in the Pearl River Delta decreased from 261.44 km²/yr during the first 10-year study period to 104.28 km²/yr in the latter three-year study period, the largest decrease of the five regions under comparison. The annual area change of built-up area in the Yangtze River Delta increased rapidly from 414.34 km²/yr during the first study period to 634.96 km²/yr in the second, the biggest increase of the five regions. The other regions did not show significant increases or decreases (Figure 7b). Compared with the period 2000-2010, although there was a small increase in the annual rate of change of built-up area in southern and central Liaoning and the Shandong Peninsula in the period 2010-2013, the annual rate of change in the other three regions fell, with the most significant fall occurring in the Pearl River Delta, where the annual rate of change decreased by 5.1%/yr between the two periods. By comparison, the annual rate of change increased by 0.51%/yr between the two periods in the Shandong Peninsula, the highest increase of all the regions in the study (Figure 7c).

By analyzing dynamic degree of built-up area, the regions with the large changes in built-up area during the two study periods were the Yangtze River Delta and the Pearl River Delta. During the latter study period (2010-2013), the dynamic degree of built-up area in the Yangtze River Delta reached 1.46%/yr, an increase of 0.51%/yr, while the dynamic degree of built-up area in the Pearl River Delta decreased by 0.63%/yr, reaching 0.42%/yr. The dynamic degree of other regions showed no significant change (Figure 7d).

Overall, since promulgation of the plan for Major Function-oriented Zones, the speed and intensity of urban expansion in the Pearl River Delta has slowed quite markedly compared to the period before the plan’s promulgation, while the spatial layout of development of built-up area was improved significantly. By contrast, the speed and intensity of urban expansion in the Yangtze River Delta and Shandong Peninsula increased rather than decreased, most notably in the Yangtze River Delta, with considerably greater annual increases than the other optimal development zones. The speed and intensity of urban expansion in the Beijing-Tianjin-Hebei region and central and southern Liaoning remained roughly the same before and after the plan’s promulgation.

Urban expansion in key development zones in the period 2000-2010 mainly took place in the eastern coastal region, central region and eastern part of the western region. Areas with the most notable urban expansion included the border area between Shandong and Jiangsu in the eastern coastal region; Changchun in Jilin and Harbin in Heilongjiang in the northeastern region; central Shanxi, northern Henan, eastern Hubei, northeastern Hunan, northern Jiangxi, and central and southern Anhui in the central region; and Erdos in Inner Mongolia, Chengdu in Sichuan, Chongqing, Kunming and Yuxi in Yunnan, and around Urumqi in Xinjiang in the western region (Figure 8a). The distribution of urban expansion in key development zones during the period 2010-2013 was similar to the decade before, with the most significant growth occurring in the eastern, central and southern parts of Anhui Province, Erdos in Inner Mongolia, Chengdu in Sichuan and Urumqi in Xinjiang (Figure 8b).

The annual area change of built-up area in the four main regions increased to varying degrees. The western region had the greatest increase in the last three years of the study period compared to the previous ten years, increasing from 326.17 km²/yr to 832.77 km²/yr. Moreover, although the overall amount of annual area change in the northeast was relatively small, it showed the greatest increase, of 2.85 times, compared to the previous decade. The eastern coastal region and northeast had the smallest increases (Figure 9b).

In the period 2010-2013, the western region had the highest annual rate of change of built-up area, reaching 6.65%/yr, and the northeastern region had the highest increase over the previous decade, from 1.10%/yr to 2.82%/yr (Figure 9c).

In terms of the dynamic degree of built-up area, the eastern coastal region continued to have the highest rate in the period 2010-2013, with 0.63%/yr, while the northeastern and western regions had the largest increases of 2.86 and 2.57 times, respectively, between the two periods (Figure 9d).

Overall, following promulgation of the plan for Major Function-oriented Zones, the average annual area of expansion of built-up area in key development zones exceeded that of optimal development zones, and all four major regions showed increases in the speed and intensity of expansion, most notably the northeastern and western regions. The western region also experienced the highest growth of all regions in terms of annual area increases and speed of growth. The eastern coastal and central regions increased at a slower rate, but urban expansion in each region was basically in line with the requirements set out in the plan for Major Function-oriented Zones.

Expansion of built-up area in agricultural production zones was relatively dispersed during the period 2000-2010, being scattered around the eastern coastal, central and southern part of northeastern regions, as well as the southeast corner of the western region. Although expansion of built-up area in agricultural production zones occurred throughout the country, overall levels were relatively low. Areas with agricultural production zones that experienced relatively high levels of expansion included the border area between Hebei and Shandong and the majority of Jiangsu and Fujian provinces in the eastern coastal region, Liaoning Province and western Jilin in the northeastern region, Henan, Anhui, Hunan and Hubei provinces in the central region, and Sichuan, Yunnan and Guizhou provinces and northern Xinjiang in the western region (Figure 10a). Compared to the previous decade, there was relatively little urban expansion in agricultural production zones during the period 2010-2013, and it was mainly concentrated in Henan, Shandong and Anhui provinces (Figure 10b).

Agricultural production zones in the eastern coastal region had the largest annual area of change in built-up area in the period 2010-2013 (590.47 km²/yr), while the western region experienced the fastest growth (442.36 km²/yr), which was 3.77 times more than the previous decade. Meanwhile, the northeastern and central regions also experienced significant increases (Figure 11b). The annual rate of change of built-up area in the period 2010-2013 was the fastest compared to the previous decade in the western region, which also had the highest overall amount, with 5.79%/yr. The rate of change of built-up area in agricultural production zones in the other three regions all showed varying degrees of growth (Figure 11c).

Agricultural production zones in the eastern coastal region also had the most dynamic built-up area, with values of 0.11%/yr in the period 2000-2010 and 0.22%/yr in the period 2010-2013, while the western region had the largest increase in dynamic condition, from 0.01%/yr in the period 2000-2010 to 0.05%/yr in the following three-year period, a five-fold increase. In addition, agricultural production zones in the central region experienced a significant increase in dynamic degree from 0.05%/yr in the period 2000-2010 to 0.14%/yr in the period 2010-2013 (Figure 11d).

Overall, since the plan for Major Function-oriented Zones was promulgated, the average annual area expansion of built-up area in agricultural production zones has exceeded that of optimal development zones. The annual rate of increase in area of built-up area in agricultural production zones in the eastern coastal, central and western regions in the 2010-2013 period was more than double that of the previous 10-year period, while the annual rate of increase in the western region was more than three times that of the previous period. Moreover, the speed and intensity of urban expansion in the four major regions also increased significantly, with the most notable increases occurring in the western region. With the exception of a few localities, the annual rate of change and dynamic degree of urban expansion in agricultural production zones in each of the main regions were below those in key development zones, which largely conformed to the requirements set out in the plan for Major Function-oriented Zones.

There was relatively little and scattered expansion of built-up area in national key ecological function zones, with less than 2% of 10 km × 10 km grids registering expansion. The little expansion that took place in the period 2000-2010 was mainly focused in eastern Hubei and the border areas of Hubei, Hunan and Chongqing in the central region, as well as eastern Inner Mongolia, southern Gansu and large parts of Shaanxi in the western region (Figure 12a). During the period 2010-2013, very little expansion of built-up area took place in key ecological function zones (Figure 12b).

Built-up area in key ecological function zones within each of the major regions expanded by a relatively small amount, with the western region showing the largest annual area of change, from 82.58 km²/yr in the period 2000-2010 to 294.69 km²/yr in the period 2010-2013, which was also the fastest rate of growth, followed by the central region, with an annual area of change 3.01 times higher in the latter period than the former (Figure 13b).

The rate of change of built-up area in key ecological function zones in the central region reached 6.66%/yr in the period 2010-2013, the highest of the four major regions. During the same period, the rate of change of built-up area in key ecological function zones greatly exceeded that of built-up area in agricultural production zones and key development zones (Figure 13c). Meanwhile, the western region experienced the largest increase in the rate of built-up area change, 3.23 times higher in the period 2010-2013 than in the period 2000-2010. The eastern coastal region had the most dynamic built-up area in key ecological function zones in both periods, being 0.02%/yr and 0.04%/yr, respectively, while the western region had the fastest growth rate in terms of dynamic condition, with the latter period 3 times higher than the former period, though the total value was quite low, only 0.009%/yr for 2010-2013 (Figure 13d).

Overall, then, following promulgation of the plan for Major Function-oriented Zones, the speed and intensity of urban expansion in key ecological function zones increased to varying degrees in each of the four major regions, with the most notable increase in the western region and the weakest growth rate in the northeastern. It is worth noting that there was a significant increase in the annual rate of change and dynamic degree of urban and rural construction in the central region, with the annual rate of change considerably higher than agricultural production zones, and even higher than key development zones. It is therefore necessary to further strengthen management and control over this.