Contour graph in python

Question

How would I make a countour grid in python using matplotlib.pyplot, where the grid is one colour where the z variable is below zero and another when z is equal to or larger than zero? I'm not very familiar with matplotlib so if anyone can give me a simple way of doing this, that would be great.

So far I have:

x= np.arange(0,361)
y= np.arange(0,91)

X,Y = np.meshgrid(x,y)

area = funcarea(L,D,H,W,X,Y) #L,D,H and W are all constants defined elsewhere.

plt.figure()
plt.contourf(X,Y,area)
plt.show()

Answer 1

You can do this using the levels keyword in contourf.

import numpy as np
import matplotlib.pyplot as plt

fig, axs = plt.subplots(1,2)

x = np.linspace(0, 1, 100)
X, Y = np.meshgrid(x, x)
Z = np.sin(X)*np.sin(Y)

levels = np.linspace(-1, 1, 40)

zdata = np.sin(8*X)*np.sin(8*Y)

cs = axs[0].contourf(X, Y, zdata, levels=levels)
fig.colorbar(cs, ax=axs[0], format="%.2f")

cs = axs[1].contourf(X, Y, zdata, levels=[-1,0,1])
fig.colorbar(cs, ax=axs[1])

plt.show()

You can change the colors by choosing and different colormap; using vmin, vmax; etc.