In the aftermath of a disaster, there is an urgent need for base maps to support relief efforts, especially in developing countries. In response to this, the OpenStreetMap project has been leveraged to produce maps of disaster-affected areas in a collaborative way. However, there has been little investigation aimed at explaining the collaborative mapping activity itself. This study presents an exploratory case study on how the collaborative mapping activities that followed the Nepal Earthquake in 2015 were coordinated and structured, i.e. how volunteers were organized, and what were the main outcomes of their activity in the context of disaster management. The results show that a large number of remote contributors spread across the world carried out concerted efforts to support the relief work. Moreover, coordination mechanisms were used by local actors to share their knowledge with remote mappers, and, hence, to improve the accuracy of the map.