# Uncertainty Analysis of Multisource Land Cover Products in China
## 3 Results
### Spatial Uncertainty  
The spatial uncertainty of the forest cover of the three products was studied. The percentage of the forest cover of the three products was calculated first, and then the two products were differentiated pixel-by-pixel. The products were divided into three groups with three resolutions, as shown in Figure 2a. The spatial distribution of the forest cover of the three products was relatively consistent but differed significantly in different regions. The North China Plain, Northeast Plain, and Xinjiang Basin in China have good consistency, with a difference in the area of less than 10%. The Greater Khingan Mountains, Southeast Hills, Hengduan Mountains, and Yunnan-Guizhou Plateau had poor consistency and more significant spatial uncertainty, with a difference in the area of more than 20%. The reason for this difference was the influence of mixed pixels in hilly areas. The impact of resolution on the uncertainty between products was explored. The percentage of various pixels varied with the resolution, as shown in Figure 2b. In general, the uncertainty between products decreased as the resolution decreased. Pixels with high uncertainty between products were counted (the difference between products was >40%). When the resolution was reduced from 0.1 to 0.3\({}^{\circ}\), such pixels were reduced by 3% on average, and the uncertainty was reduced. The low-uncertainty pixels were counted (the difference between products was >10%). This type of pixel increased by 5.8% as the resolution decreased. CCI-VCF had the fewest high-uncertainty pixels, accounting for 0.1% of the total pixels, while the low-uncertainty pixels were the most numerous, accounting for 81% of the total pixels. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Land Cover** \\ **Type** \\ \end{tabular} } & \multicolumn{2}{c}{**ESA CCI**} & \multicolumn{2}{c}{**MCD12**} & \multicolumn{2}{c}{**VCF**} \\ \cline{2-7}  & **Area (\%)** & \begin{tabular}{c} **Coefficient of** \\ **Deviation** \\ \end{tabular} & **Area (\%)** & \
\begin{tabular}{c} **Coefficient of** \\ **Deviation** \\ \end{tabular} & **Area (\%)** &
\begin{tabular}{c} **Coefficient of** \\ **Deviation** \\ \end{tabular} \\ \hline Forest & 13.24 & \(-\)0.1222 & 17.62 & 0.1677 & 14.40 & \(-\)0.0456 \\ Nontree vegetation & 48.76 & 0.0952 & 45.81 & 0.0287 & 39.01 & \(-\)0.1239 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Sample selection categories and data statistics. The spatial uncertainty of the nontree vegetation cover of the three products was studied. The percentage of the nontree vegetation cover of the three products was calculated first, and then the two products were differentiated pixel-by-pixel. The products were divided into three groups with three resolutions, as shown in Figure 3a. More significant differences appear in different regions, with great uncertainty. For example, the nontree vegetation of VCF products in the Qinghai-Tibet Plateau was more than 40% different from that of the other two products. The reason is that under the VCF classification system, the percentage of nontree vegetation in the Qinghai-Tibet Plateau was considered to be large, while the other two products showed very little nontree vegetation there. The nontree vegetation coverage of ESA CCI products and MODIS products in the North China Plain was relatively consistent, with an area difference of less than 10%, while the difference  
Figure 2: Spatial difference in forest coverage among the three products. Panel (**a**) shows the resolution and spatial difference between products, “CCI\(-\)MODIS” represents the difference between the forest percentage of ESA CCI and MODIS products, the horizontal is the product consistency comparison, and the vertical is the consistency comparison of different resolutions. The darker the color, the greater the product difference. Panel (**b**) shows the PFT statistics and the percentage of various pixels with the change in resolution.