how to color cells according to the points number

Hi everyone,

I am just starting learning GH. Now there are several points on my map and I m going to using grid to divide the map. Then I want to count the point in each cells and highlight it in different colors. But I don't know how to achieve it using GH. Is there any one can help me.

further more, I would like to know if i can draw circles in the cells and each circle's radium depends on how many points in the cell.  The attachment shows the outcome that I intend to reach.    

Thank you!