A good strategy for these kinds of plots is to treat it as if the numbers are 1 to 15, and then just change the labels
y=rand(1,15);
x=1:15;
scatter(x,y,'x')
set(gca,'XTick',1:15,'XTickLabels',1:3)
for i = 1:5
xline(i*3+.5,'Label',"ZONE " + i, 'LabelHorizontalAlignment', 'left')
end
box on
But you can also use tiledlayout effectively for this kind of thing by setting the TileSpacing property to 'none'
figure
t=tiledlayout(1,5,'TileSpacing','none');
for i = 1:5
scatter(nexttile,1:3,rand(1,3),'x')
ylabel("ZONE " + i) % you might want to use the text function for the labels...as this is awkward
box on
end
linkaxes(t.Children)
xlim([.5 3.5])
set(t.Children(1:4), 'YTickLabel', [])
xlabel(t,'Case Number')
