Assessment of the completeness of Volunteered Geographic Information focusing on building blocks data (Case Study: Tehran metropolis)

Open Street Map (OSM) is currently the largest collection of volunteered geographic data, widely used in many projects as an alternative to or integrated with authoritative data. However, the quality of these data has been one of the obstacles to the widely use of it. In this article, from among the elements related to the quality of volunteered geographic data, we have tried to examine the completeness of building block data in the OSM for Tehran metropolis. In order to do it,  we have applied two object-based and unit-based approaches that are frequently applied in similar studies. The findings of this study demonstrate that the estimation of OSM building completeness strongly differs from these two approaches. The results demonstrate the high speed of evaluation of the unit-based approach and the higher accuracy of object-based method. Moreover, the results for the unit-based method indicate that a unit-based comparison of the total number or area of buildings is highly sensitive to disparities in modeling. While the object-based methods have lower sensitivity than disparities in modeling and if the data have an appropriate location accuracy, they will provide more accurate results for the completeness parameter. Therefore, the recommendation of this paper is to use an object-based method in quality assessment studies. In the end, based on the object-based approach, the parameter of completeness in the whole study area was calculated as 2.7%, which shows a low rate of completeness. Evaluating the results in closer detail,  shows that the northern, central and eastern parts of Tehran are more complete than the other parts. Also, in most regions of Tehran, more than 80% of the official data is not in the OSM dataset, which indicates that the official dataset is more complete than the OSM one.