A map has a size of 3000x2000 pixels. Planning a path on a pixel base would take very long. Even an efficient algorithm will need to compute many possible graphs. The reason is, that such a map would contain 6 million pixels overall and the possibilities to explore the geometrical space are exceedingly large. The first step for a hierarchical path planner is to divide the map into smaller sub-maps. Each cluster has a size of 300x200 pixel. The number of clusters overall is 10x10=100. In the newly created graph the amount of nodes is small, it is possible to navigate between the 100 clusters, but not within the detailed map. If a valid path was found in the high-level-graph the next step is to plan the path within each cluster. The submap has 300x200 pixel which can be handled by a normal A* pathplanner easily.