Cell growth isn't independent of the cells around them.

For example if you get cut the cells around a gap will send out external signals (send and pray) which might cause other cells to start growing. Once the gap is filled (i.e. the cells are adjacent to each other) the surrounding cells will again send out signals to tell them "Stop! Space is getting tight!".

Sometimes its also the other way (or a combination of both) and a cell will detect an empty area and grow.

Here's a link to a game to show how cell growth works: http://nobelprize.org/educational_games/medicine/2001/cellcy...