# A Multilevel Road Alignment Model for Spatial-Query-by-Sketch
## 4 Results and Discussion
### Discussion  
As indicated in Table 5, all the sketch maps could be used to query the accurate corresponding roads from OSM, except for S7. The key experimental results are as follows.  
Although the roads were drawn partially or distorted in several sketch maps, accurate matching results could be obtained, including those for sketches S1, S2, S4-S6, S8, and S9. In Table 5, S1 has one partially drawn road (red line), but an accurate metric road map was observed in the top matching result. This finding also holds for S2, S4, S5, and S9 (having a partially drawn road in red, blue, green, and purple, respectively). Furthermore, the accurate matching results of these sketch maps were in the top three results.  
Accurate matching results could also be obtained for sketch maps with distorted roads. For example, in S4, all the main roads were drawn in a distorted manner except for the one in blue; nevertheless, the exact match was in the second place (see Table 5). S6 (distorted road in green)  
Figure 18: Time cost for roads matching in each sketch.  
and S8 (distorted road in purple) also exhibited accurate matching results in the third and first places, respectively.  
Accurate matching results could be obtained for sketch maps involving inconsistent topological relationships between roads with those in the metric map. In S5, two roads (in red and blue) were drawn inconsistently with those in the metric map, which led to an inconsistent topological relationship see Figure 19. Thus, two rows of matching results were shown for sketch S5, in which one row shows the matching results obtained considering the topological relationship between these two roads, while the other row shows the results obtained not considering this relationship (see the two rows of matching results for S5 in Table 5). Nevertheless, an accurate matching result (\(Sim_{SR}\) = 201.744) was obtained, even when the topological relationship between the two roads was not considered (see the first row of matching results for S5 in Table 5).  
Accurate road maps could not be obtained for S7 from OSM, as shown in Table 5. This can be attributed to the small number of roads (only 2) drawn in the sketch and the fewer curves of these roads (see Table 4).  
In particular, the characteristic _first matching priority_ (\(FMP\), see Section 3.3.1) can be assigned to a road with more shape curves and a higher _degree centrality_ value in one sketch map. More curved shape can improve the similarity in computing _shape distance_. A higher _degree centrality_ value means more roads connected to this road as we discussed in Section 4.1 and correspondingly involves more composite roads matchings. For example, in sketch S1, green road is more curved than other main roads extracted. Furthermore, its _degree centrality_ value (3) is the highest as Table 5 shows. This holds for the same road in sketches S2-S7 and S9. Whereas in sketch S8, the same road (in purple) is a straight line, so \(FMP\) was assigned to the road in green. Characteristic \(FMP\) can help narrow the search range, as demonstrated in Section 3.3.1.