I had the same need, so what I did was to add one extra point in my map with a reference velocity. Then I added some text close to this "reference arrow" to explain it. Of course, some empty space on the map is needed. Basically, it would be as follows:
[x,y] = meshgrid(0:0.2:2,0:0.2:2);
u = cos(x).*y;
v = sin(x).*y;
figure
But then:
%An additional row of points is added at y=2.2:
[X,Y]=meshgrid([0:0.2:2],2.2);
%Then a reference arrow velocity is defined at x=0.2 and y=2.2, while rest of points are left as zero:
u_rf=zeros(1,11);
v_rf=zeros(1,11);
u_rf(1,2)=1;
%Thus, quiver plot is applied including the new row:
quiver([X;x],[Y;y],[u_rf;u],[v_rf;v]); %is done like this to be sure we got the same arrow AutoScale
%Finally some text is included:
text(0.05,2.3,'Arrow scale: 1m/s')
Resulting in the following plot:
I hope it may help someone, as this post it quite old.
Felipe.
