## 3 Results
### Cumulative Relationship of PLES and Endowment Factors Level
#### 3.3.1. Cumulative Relationship of PLES and Natural Factors Level  
Figure 5a-c represents the cumulative curve of the elevation, relief intensity and distance to water in the overall and PLES types, respectively. Among the dispersion of curves, the difference among the four curves in Figure 5a is the largest. In particular, there is almost no difference in the distance to water in Figure 5c. In Figure 5a, the LS curve was higher than the other three. The tangent point of the curve with slope one was defined as the segmentation point. Before the segmentation point, the rate of area accumulation was faster than 1%, and after, it was the opposite. When the accumulation level reached 95%, the critical point was defined, based on the thought that 95% of the space of each type could represent most of the characteristics of that type. When the elevation level reaches only 6%, the LS curve reaches the segmentation point, and the accumulation is completed at 85.81%. The segmentation point of PS appears when the elevation index is 6%, but only 67.75% is accumulated. For the same elevation suitability, the accumulation ratio of PS was lower than that of LS, because the living function was in a leading position in rural areas, which caused a higher priority in functional selection. Due to the effect of PS and LS, the segmentation point of the study region appears at the level of an 8% elevation, and the total accumulation is less than 48%. In sharp contrast, the segmentation point of ES appeared at the 53% elevation level, which accumulated more than 90%. The critical points of the four curves in Figure 5a appeared at 28%, 50%, 52% and 57%, respectively. This suggests that LS and PS are appropriately distributed below 6% of the regional elevation level. When the elevation exceeds 28% and 50%, there is almost no LS and PS. The space between the segmentation point and critical point is of suitable scope. The scope of the ES suitability  
Figure 8. Sankey diagram of PLES area from 1980 to 2018.  
Figure 7. PLES cumulative curves of facilities. (**a**) Distance to interchanges; (**b**) distance to roads.  
was minimum, and changes in the elevation had little influence. The ES is distributed over a space that is hard to use, so it deserved a relatively lower position. Figure 5b showed that the accumulation performance of relief intensity was different from that of elevation. The segmentation levels of LS, ES, study region and PS are located at 6%, 12%, 24% and 30%, respectively. LS has the greatest dependence on lower relief. The accumulation of the four lines at the segmentation point is over 90%. The critical points were close to the segmentation points. This was because the relief intensity was mainly distributed in the low-level range, and the high relief area was small. The cumulative level of LS was 95.79%, and the critical point was lower than the segmentation point. In addition, the curves of LS and PS were closer to the Y-axis below the segmentation level, and the ES curve was farther from the Y-axis. It can be seen that the space with low relief intensity was mainly occupied by LS and PS, which is similar to the results of the elevation curves. Figure 5c shows the accumulation of the distance to water. The segmentation points of the four curves are in the horizontal range of 18-21%. The accumulation of PS was higher than that of LS and ES before 7%. When it exceeded 22%, ES became the highest accumulation type. Although the difference among the curves is small, there are still differences in different horizontal stages.