# A Multilevel Road Alignment Model for Spatial-Query-by-Sketch
## 5 Conclusions and Future Work  
This paper proposes a shape-based approach for spatial-query-by-sketch, known as Shaped-based Spatial-Query-by-Sketch. In the work by [PERSON] et al. [24], it was noted that main roads exhibit considerable similarities between the sketch maps and the metric map. Considering this aspect, in this work, the data for main roads were obtained from sketch maps based on two factors, namely, the _degree centrality_ and _betweenness centrality_. Subsequently, the main roads were compared in three levels quantitatively and qualitatively--individual road, composite road, and road scene. In the first level, we calculated the similarities between two individual roads considering quantitative characteristics, such as _the shape distance_, and qualitative characteristics such as _the circulation direction_. In the second level, the _topological relationship_ and quantitative characteristics of a composite road (i.e., composed of two individual roads), such as _the relative positions of the intersections_, were aligned between the sketch maps and the metric map. In the third level, all the main roads extracted from a sketch map were further quantitatively and qualitatively compared with those in the metric map based on the road scene characteristics, e.g., _the frequency of a matched road_. Next, the matching results were sorted based on the sum of the characteristic similarities. An experiment was performed, in which nine sketch maps drawn by nine participants were aligned with the metric map derived from OSM. The results  
Figure 19: Different topological relationships of the corresponding two roads in OSM and S5. indicated that for eight out of nine sketch maps, accurate road maps could be obtained from the metric map. The inaccurate matching of the remaining sketch map was a result of the small number of roads in the sketch (only 2) and the presence of only a few shape curves in the roads. Furthermore, it was noted that accurate matching results could be obtained for sketch maps with partially drawn roads or distorted roads and even for roads with an inconsistent topological relationship with those in the metric map. The following aspects are expected to be a part of future work:  
* Comparison of the spatial relationship between roads and buildings, such as the orientation relationship, topological relationship, and ordering relationship. In particular, in some sketches, only a few roads are drawn, which makes it challenging to match these roads. Combining the sketched roads with buildings may improve the accuracy of matching. * Development of a method to match the sketched places with discrete sketched roads. Discrete sketched roads are road segments generated during the process of digitization. Specifically, in this work, the roads in the sketch maps were digitized manually and the road integrity was guaranteed. In future work, the digitization will be conducted automatically, by decomposing the roads in the sketch maps into several line segments. Note that the shape of a discrete sketched road may be different from that of a completely sketched road, and the topological relationship between such roads may also be different. Therefore, in future work, we intend to realize matching between discrete sketched roads and complete roads in the metric map. * Application of the proposed model to an unknown experimental area. In this study, the road similarity was examined considering roads in familiar places. An objective of future work is to study the characteristics and consistency of roads in unfamiliar scenes. Conceptualization, M.T., Z.F., and Y.S. ; methodology, M.T. and Z.F. ; software, M.T. ; validation, M.T. ; formal analysis, M.T. ; investigation, M.T. and Z.F. ; resources, M.T. ; data curation, M.T. ; writing--original draft preparation, M.T. ; writing--review and editing, Z.F. and Y.S. ; visualization, M.T. ; supervision, Z.F. and Y.S. ; project administration, Z.F. and Y.S. ; funding acquisition, Y.S. All authors have read and agreed to the published version of the manuscript.