You place figure and hold on line outside the loop:
figure('Name', 'Pax per Hour');
hold on;
for k = 1:24
for i = 1:30
for j = 1:30
hrVal = zeros(1,1);
if ~isempty(gridPax{i,j})
hrVal = log(gridPax{i,j}(k)+1);
end
hrPax{i,j} = hrVal;
end
end
x = linspace(103.6,104,30);
y = linspace(1.5,1.25,30);
[X,Y] = meshgrid(x,y);
Z = cell2mat(hrPax);
% interpolate to a finer grid
newG = 200;
xq = linspace(103.6,104,newG);
xy = linspace(1.5,1.25,newG);
[Xq,Yq] = meshgrid(xq,xy);
Zq = interp2(X,Y,Z,Xq,Yq,'cubic');
surf(Xq,Yq,Zq);
xlabel 'Latitude'; ylabel 'Longitude'; zlabel 'No. of Pax';
axis tight
colormap default
drawnow
end
