How to fit Spy plot on whole figure screen ?

Hello

I have a square matrix m X m with 1's and 0's. I want to plot this matrix, such that there is a dot wherever 1 is mentioned in the matrix.

I came across spy function to plot sparse matrix. However, it does not fit onto whole figure screen, which creates overlapping of X and y labels in the plot.

Questions:

How can I fit the square shaped spy plot to the whole figure window / screen ? How can I make grids on this "spy plot" ? At the bottom of the spy plot, "nz" is mentioned. What is meant by nz ??

Thanks