Matplotlib evenly spaced contour lines

Question

I'm learning how to use the contour function and I was assigned the task of plotting 25 evenly spaced lines using a 4th parameter.

Edit: This is the desired image:

z = np.load('heights.npy')
plt.contour(np.transpose(z), 25) #Now plotting with 25 evenly spaced contours
plt.title('even contour lines')
plt.savefig('myFig2.png', format='png')

I've checked here and I can't find what I need. Any help would be appreciated thanks.

I've also looked here but as you can see, my lines are not evenly spaced.

I'm pretty sure "evenly spaced" means "with respect to level value". Unless your function is linear, these equilevel curves (dunno what the proper name is) will never be actually evenly spaced in the `(x,y)` plane. Or am I misunderstanding something? — Andras Deak -- Слава Україні, Oct 10 '15 at 23:59
In the sample image I am to produce, the lines are evenly spaced — Brian B., Oct 11 '15 at 00:01
Have you also checked `help(plt.contour)`? It says `contour(X,Y,Z,V) - draw contour lines at the values specified in sequence *V*`. Have you tried providing an equidistant list `V`? — Andras Deak -- Слава Україні, Oct 11 '15 at 00:17
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/91941/discussion-between-brian-b-and-andras-deak). — Brian B., Oct 11 '15 at 01:05

score 4 · Accepted Answer · answered Oct 11 '15 at 01:13

You need to manually specify the levels for your plot, otherwise matplotlib will determine the levels for you, which is clearly not what you want.

z = np.load('heights.npy')
plt.contour(np.transpose(z),np.linspace(z.min(),z.max(),25)) 
plt.title('even contour lines')
plt.savefig('myFig2.png', format='png')

This will set the contour levels such that it divides the span of your z data to 24 equidistant intervals, giving 25 lines.

Matplotlib evenly spaced contour lines

1 Answers1