Constructing a grid larger than 60 by 60 boxes

Hi,

I am trying to construct a large grid (210 *130) but am limited by the
number of ticks i can use (60). Is there any way to do this? I am
using polyfill to draw approximately 26,000 boxes and want to use the
PLOT command, specifying the number of ticks and making the length
cover the whole plot to draw an outline around each box.

thanks,

Clive