MATLAB: Adding a matrix layer to an already existing matrix

Question

I want to add a layer to my 180×180 matrix, seen below. N is where I define the actual matrix in the code. I want to add a layer to make it a 3D matrix such that the second layer has a cell value of 0 at (90,90) and increases by 1 for increasing i and j indices, and decreases by 1 for decreasing i and j indices. So I am essentially setting up a cartesian coordinate plane with the second layer. so the index (91,90) should have a value of 1, (92,90) a value of 2, (89,90) a value of -1, (90,91) a value of 1, etc. Any ideas?

N1 = randi([1,500],45,45);
N2 = randi([25,1000],45,45);
N3 = randi([100,2200],45,45);
N4 = randi([5,700],45,45);
N5 = randi([100,500],45,45);
N6 = randi([800,3500],45,45);
N7 = randi([1000,10000],45,45);
N8 = randi([15,1000],45,45);
N9 = randi([250,900],45,45);
N10 = randi([5000,11000],45,45);
N11 = randi([1750,9000],45,45);
N12 = randi([25,890],45,45);
N13 = randi([2000,7500],45,45);
N14 = randi([200,2300],45,45);
N15 = randi([25,750],45,45);
N16 = randi([50,1323],45,45); 
N = [N1  N2  N3  N4;
     N5  N6  N7  N8;
     N9  N10 N11 N12;
     N13 N14 N15 N16];

Answer 1

M(:,:,2) = bsxfun(@plus,-89:90,(-89:90).');