*3.8. Grid-Based Methods*

Grid-based methods are classified as approximate cellular decomposition due to the restriction of the grid's shape, which is uniform in space. It is impossible to represent precisely the shape of the target space and its obstacles [19]. The grid-based methods decomposed the space into uniform grid cells, which can be squares or other shapes, as shown in Figure 7. Moravec and Elfes [49] proposed a grid map presentation based on a sonar mounted on a mobile robot mapping an indoor environment.

**Figure 7.** Grid-based decomposition.
