## 5 Discussion
### GDP Variation Pattern Analysis based on the Clustering Results  
Based on Chinese land use/cover datasets from 1995, 2000, 2005, and 2010, three land use types--including urban built-up area, rural residential area, and industrial area--were counted for each clustering class. Figure 8 illustrates the statistical results of the three land use types for each class. A comparison of Figure 8a-c indicates that the main land use type in the first class is urban built-up area, which suggests that the first class is associated with urban centers in large, medium, and small cities. The main land use type of the second and third classes is rural residential area. However, urban built-up area is much more common in the second class than in the third class. Therefore, the second class is generally associated with urban fringe areas, and the third class is associated with areas in the countryside.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Year** & **RMSE** & **MRE** & **R** \\ \hline
1997 & 4.9614 & 4.5572\% & 0.9982 \\
1998 & 3.6867 & 3.0326\% & 0.9992 \\
1999 & 1.8850 & 1.8516\% & 0.9988 \\
2000 & 4.2335 & 3.3435\% & 0.9949 \\
2001 & 3.2224 & 2.5797\% & 0.9989 \\
2002 & 3.3361 & 2.1376\% & 0.9995 \\
2003 & 10.9458 & 6.1353\% & 0.9729 \\
2004 & 8.1877 & 4.0032\% & 0.9895 \\
2005 & 28.8478 & 11.4043\% & 0.9649 \\
2006 & 14.3577 & 5.1784\% & 0.9929 \\
2007 & 22.5479 & 7.4647\% & 0.9826 \\
2008 & 17.6268 & 4.3592\% & 0.9934 \\
2009 & 12.5426 & 2.8741\% & 0.9969 \\
2010 & 19.7350 & 3.8184\% & 0.9935 \\
2011 & 48.0933 & 7.6910\% & 0.9694 \\
2012 & 68.3982 & 9.3377\% & 0.9468 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Three statistical measures based on estimated and actual GDP in the 13 districts/counties of Wuhan (GDP unit = 100 million RMB).  
Figure 9 shows the GDP variations in the above three classes over time. In Figure 9, the \(x\)-axis categories represent the clustering classes, and the GDP variations represent the change in the average GDP of each class in two adjacent years. The overall GDP variation in the study area was relatively minor before 2007, and rapid growth occurred after that point. The cause of this growth was the approval of the Wuhan Metropolitan Area as a reform area with a resource-conserving and environmentally friendly society in 2007. The establishment of reform policy promoted economic connection and integration between the cities in the study area.  
Figure 8: The statistical results of three land use types for three clustering classes in four years: (**a**) The first class; (**b**) The second class; (**c**) The third class.  
Differences in the GDP variation pattern of each class can be observed from 1992 to 2012. The GDP variations of the first class, representing urban centers, fluctuated considerably. Before 2007, because the government took the lead in developing the economy in eastern coastal areas, urban economic development in the study area slowed and even regressed. At that time, due to policy impacts, many resource-intensive industries relocated, which caused the GDP to briefly decline. Since then, with the development of urbanization and tertiary industry growth, GDP growth has significantly accelerated. The second class represents the GDP change in urban fringe areas. Before 2007, the GDP variations in these regions were small because these undeveloped areas were dominated by primary industry. Then, with the acceleration of urbanization and industrial structure transformation caused by industry migration, secondary and tertiary industries became active in these areas and led to rapid GDP growth. The GDP development of the third class was stagnant because these areas are distributed in rural areas. The small GDP increase in these areas was associated with the radiation effect of GDP growth in the Wuhan Metropolitan Area. Moreover, due to the continuous development of agricultural production technology, the GDP increased in areas engaged in primary industry.