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Why can't I display a line on a plot (can only have points marker)

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I'm trying to plot a line (x1,y1) on a plot where I applied a mask for land (green) and seas (blue). Whatever the LineSpec I try to use it only displays marker points instead of a line.
I tried to plot the three different options below (plt1, plt2, plt3). I get (x1,y1) in the first case, but it displays points instead of a continuous line as expected (matlab_fig1.png). In the second (matlab_fig2.png) and third case (matlab_fig3.png), I don't get anything.
Here is my code:
%Plot in cartesian coordinates
%Make Land mask
load([pwd '/Grid/bathyEASE.mat']); % load bathymetry
hold on; box on;
xlim([0 361]);
ylim([0 361]);
shading flat;
axis ij;
x1 = [159:163];
y1 = 77;
plt1 = plot(x1,y1,'-r','LineWidth',3,'Marker','.','MarkerEdgeColor','r'); %Refer to --> matlab_fig.png
%plt2 = plot(x1,y1,'-r','LineWidth',3); %Refer to --> matlab_fig2.png
%plt3 = plot(x1,y1); %Refer to --> matlab_fig3.png
Thank you

Accepted Answer

dpb on 28 Jun 2021
Edited: dpb on 29 Jun 2021
x1 = [159:163];
y1 = 77;
plt1 = plot(x1,y1,'-r','LineWidth',3,'Marker','.','MarkerEdgeColor','r');
When you plot() a vector of one variable against a constant in the other, plot creates a line object for each element of the vector and a single pixel marker simply isn't large enough to show up; there is no line created because there are (in this case 5) separate line objects, each consisting of only a single point.
You also have the sequence of commands in wrong order; or you need a hold on first after setting the axes limits and orientations or plot will cause refreshing the limits of the plot to match the plotted data.
If you want to plot a single vertical or horizontal line; the xline or yline functions are the better way to do so; they're relatively recent but get around the need to duplicate the constant data value manually (but cross the entire axis in extent so not helpful here -- Addendum/Correction --dpb)
Try something more like
xlim([0 361]),ylim([0 361])
axis ij
hL=plot(x,repmat(y,size(x)),'-r','LineWidth',3); % ammended remove yline call -- dpb
and joy should ensue.
dpb on 28 Jun 2021
Oh, yeah, I forget (that's what happens with age, it seems, I don't recommend it! :) )
Indeed, x/yline do go from one edge of the axes to the other -- but note that you only need the first and last points to draw a straight line, not all the intermediary ones.
xlim([0 361]),ylim([0 361])
axis ij
hold on

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