In this paper, we propose a novel sensor data collection method using an overlay network that forwards collection request messages to the sensor nodes which have sensor data needed to create interpolated contour lines maps. When there is an enormous number of sensor nodes, it is redundant to collect all sensor data from a target area since geographically close sensor data can be interpolated. Moreover, since the interpolation process requires heavy CPU load, the process may not be finished

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... n a reasonable time period if too much sensor data arrived. On the other hand, there is a trade-off between the number of collected sensor data and the accuracy of the created contour lines map. In our proposed method, the number of collected sensor data can be limited to a constant number. At the same time, granularity of characteristic points in the contour lines maps can be specified by users in order to satisfy the various requirements. Our proposed method extends the hierarchical Delaunay overlay network (HDOV) and forwards the collection request messages according to the feature amounts that correspond to the characteristic points for each layer of the HDOV. Simulation results showed that our proposed method could create contour lines maps while satisfying the requested granularity of the characteristic points within the constant number of sensor data.