All great information.
Additionally, a "cell" is at the intersection of three cell antenna towers, allowing resonably accurate location triangulation (even without GPS), and providing coverage even when in a "shadow" from a large building that blocks coverage from one or two of those cell towers:
And as shown in the above diagram, each tower covers three cells, as you can see in this image:
Of course, this is just a general rule. In reality, there are a lot of variations that are needed to cover unusual circumstances, such as for filling in coverage "holes" created by local obstructions and unusual geographic topography.