Due to the small size of Micro Aerial Vehicles, they are well suited for various indoor applications, especially search/rescue operations. Most of these operations are performed in unknown 3D environments. Real‐time map construction and vehicle's localization are essential tasks. Various approaches provide solutions for 3D‐map representation. However, these approaches require expensive embedded systems to afford high‐processing memory/computational costs. Because of its exposure to risks, the MAV should be equipped with a low‐cost navigation system. The principal aim of map construction herein is to facilitate the navigation task. Thus, constructing a massive 3D map is not required. Consequently, this paper proposes an efficient real‐time 3D SLAM. The proposed method avoids the 3D‐map representation of each region of the trajectory. Alternatively, it divides the environment along the trajectory into several 2D maps with a single 2D map in every region at the height of the MAV, as well as a transient region between each of the two constructed maps to enable connecting neighboring maps.