CoMapping is a framework to efficient manage, share, and merge 3D map data between mobile robots. The main objective of this framework is to implement a Collaborative Mapping for outdoor environments. The framework structure is based on two stages. During the first one, the Pre-Local Mapping stage, each robot constructs a real time pre-local map of its environment using Laser Rangefinder data and low cost GPS information only in certain situations. Afterwards, the second one is the Local Mapping stage where the robots share their pre-local maps and merge them in a decentralized way in order to improve their new maps, renamed now as local maps. An experimental study for the case of decentralized cooperative 3D mapping is presented, where tests were conducted using three intelligent cars equipped with LiDAR and GPS receiver devices in urban outdoor scenarios. We also discuss the performance of the cooperative system in terms of map alignments.