Cell Spots
Cell spots, also known as sub-cells, are sub-units of a map cell used in infantry pathfinding, and in Tiberian Sun, warhead Spread calculations. A cell constitutes of five cell spots, one for the center and one for each corner. Infantry may occupy and move freely between cell spots, allowing for multiple infantry units to fit into one cell. In Tiberian Dawn and Red Alert all five spots are used.
Broken Spots
In Tiberian Sun through Yuri's Revenge, the first two spots (0 and 1) appear unused, overlapping at the center of the cell. Infantry can normally only occupy the last three cell spots (2-4), i.e. the east, west, and south corners of the cell. However, infantry may sometimes appear at the center of the cell, for example when spawned on the map, ejected from a transport or placed by the map editors, but they are unable to move back to that spot.
Because the top corner of the cell has no cell spot, infantry cannot occupy it. They may still freely move through it, provided the adjacent spots are not occupied by terrain objects or other infantry.
Bugs/Side-Effects/Unexpected Limitations
The FinalAlert map editor (and its derivatives, like FinalSun) cannot display infantry that are preplaced at spot 4. Care should be taken when editing vanilla maps, as they may contain infantry on that spot.