# Selection of Grid Road Networks Based on Raster Data
## 4 Experiments and Evaluations
### Experimental Results and Analysis
In Figure 10, the grey parts mark the removed road segments, while the selected road segments are marked with the orange color. The conventional vector-based ArcGIS technique cannot effectively maintain the road branches that are directly connected with the main road since it cannot automatically identify main roads with larger widths, such as the removed road segments within the areas delineated by crimson rectangles in Figure 10a,c. However, as the proposed AWRS method can automatically distinguish the main roads according to the actual road widths, it performs better in the local connectivity preservation of road branches that are directly connected with the main road, like the areas outlined by green rectangles in Figure 10b,d;
4. **Road completeness preservation**. In road network selection, the remaining roads should have a more complete structure rather than be presented as separate segments. Figure 11 shows the differences in the road completeness preservation using the ArcGIS and AWRS methods, and we can see the following. The traditional ArcGIS selection method is prone to producing isolated road segments, like the selected road segments in Figure 11a, and disconnected road segments, like the selected road segments in Figure 11c, which displays a poor road completeness preservation ability. However, the proposed AWRS method can avoid generating separate segments and preserve a more complete road structure. Some typical examples can be seen in the green rectangles in Figure 11b,d, which show a good road completeness preservation ability. Figure 8: Differences in semantic feature preservation using the ArcGIS and AWRS methods. (**a**) ArcGIS. (**b**) AWRS. Figure 9: Differences in global structure preservation using the ArcGIS and AWRS methods. (**a**) ArcGIS. (**b**) AWRS. To quantitatively evaluate the vector-based ArcGIS and raster-based AWRS methods of road network selection, we used three indicators to measure the differences in the performances: the geometrical similarity (\(GS\)) of the road networks, the topological connectivity (\(TC\)) of the road intersections, and the preservation degree (\(PD\)) of the hub nodes at different road levels. The \(GS\) indicator of road networks is usually utilized for measuring the shape consistencies of elements during the selection operation [17] and can be calculated using the following equation:  
\[GS=\frac{A\cap B}{(A\cup B)-(A\cap B)} \tag{6}\]  
Figure 11: Differences in road completeness preservation using the ArcGIS and AWRS methods. (**a**) Region 1 using ArcGIS method. (**b**) Region 1 using AWRS method. (**c**) Region 2 using ArcGIS method. (**d**) Region 2 using AWRS method. Figure 10: Differences in local connectivity preservation using the ArcGIS and AWRS methods. (**a**) Region 1 using ArcGIS method. (**b**) Region 1 using AWRS method. (**c**) Region 2 using ArcGIS method. (**d**) Region 2 using AWRS method. where \(A\) represents the length (area) of the road networks after selection, \(B\) represents the length (area) of the road networks before selection, \(A\cup B\) represents the total length (area) of the road networks before and after selection, and \(A\cap B\) represents the length (area) of the overlapped road networks before and after selection. As shown in Table 1, the original length of the road network centerlines handled by the ArcGIS method is 487,520 m. After selection using the ArcGIS method, the lengths of the selected road segments at the two target levels are 361,849 and 251,237 m, which are reduced by 25.8% and 48.4%, respectively. The original area of road networks handled by the proposed AWRS method is 524,371. After selection using the proposed AWRS method, the areas of the selected road segments at the two target levels are 479,841 and 359,744 pixels, which are reduced by 8.5% and 31.4%, respectively.