I am looking for some help or code for the following (it must have been done many times before but I don't quite know how to word a search):

I have a series of values with x,y coordinates;
23,5
31,19
47,7
etc
and a grid which is from 20-50 in steps of 10 along x and 0-20 in steps of 2 along y.
I want to find which cell each point is in (and the center of that cell).
Eg the first point falls in cell x1, y3 with center at x=25, y=5
Any help or suggestions where to look would be greatly appreciated
Thanks