Here's an example:
% create vectors for x/y non/oscillatory
n = 5;
o_idx = [1 2 6 7 8 11 12 16 21 22];
[xo,yo] = meshgrid(1:n);
xo = xo(:);
yo = yo(:);
xn = xo;
yn = yo;
idx = ismember(1:n^2,o_idx);
xo = xo(idx);
yo = yo(idx);
xn = xn(~idx);
yn = yn(~idx);
% plot the points
figure
plot(xo,yo,'.r','MarkerSize',12)
hold on
plot(xn,yn,'.c','MarkerSize',12)
xlim([0 n+1])
ylim([0 n+1])
% make a contour dividing the regions
c = zeros(n);
c(idx) = 1;
contour(c,'LevelList',0.5,'Color','k')
