Adding contour lines to heatmap

Using a 100X100 matrix, I have genertated this heatmap (attached fig). The deepest shade of red indicates a frequency of 25. And deep blue indicates a frequency of 0.

How will I add a line (a circle) to show encircle the area covers 90% of my data?

I want to compare multiple such figures..so such contour lines will be very useful for me.

Thanks in advance!!

Answer 1

[KSSV]

Read about contourf.

Or use contour with hold on. You need to specify the level and your desired color.

[Ishani Mukherjee]

Thank you so much!!.. this connects points with similar values..is there any way I can encircle all points above a certain value ?

I also want to keep the heatmap intact..just make contour lines on top of it..not convert it to a contour plot.

[KSSV]

Let X, Y, Z be your data matrices.

idx = Z<=1 ;  
x = X(idx) ; y = Y(idx) ;
idxb = boundary(x,y) ; 
pcolor(X,Y,Z)
shading interp
hold on
plot(x(idxb),y(idxb),'k')

[Ishani Mukherjee]

Thanks..

[KSSV]

Then what is 100*100 matrix in the question? How can you generate such plot without a matrix?