matplotlib box on basemap map - graphics

Question

I'm trying to draw a box on a map in relative coordinates (i.e. 0 to 1). The reason is I have a colorbar on my map, but cannot see it clearly. I want a transparent box behind it. I've looked at adding patch Rectangles (see Draw rectangle (add_patch) in pylab mode), but that is in data coordinates, which is not easy to determine on this map. I also found axhspan, which uses relative coordinates for the x span, but data coordinates for the y span.
Is there a way to draw a box in a matplotlib axes object using relative coordinates?

Answer 1

Here's a way to add a boxed text to a relative coordinates:
#!/usr/bin/python3
from matplotlib import pyplot as plt
x = range(5)
y = range(5)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x, y)
ax.text(0.5, 0.5,
"Relative coords!",
horizontalalignment = 'center',
backgroundcolor = "white",
verticalalignment = 'center',
bbox=dict(facecolor='white', edgecolor='green', alpha=0.65),
transform = ax.transAxes,
)
fig.savefig("mwe.png")
Result:
Edit:
To draw just a box given it's relative coordinates/dimensions with no text in it:
#!/usr/bin/python3
from matplotlib import pyplot as plt
from matplotlib.patches import Rectangle
x = range(5)
y = range(5)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x, y, zorder=1)
plt.gca().add_patch(Rectangle(
(0.4, 0.4), # lower left point of rectangle
0.2, 0.2, # width/height of rectangle
transform=ax.transAxes,
facecolor="white",
edgecolor='green',
alpha=0.65,
zorder=2,
))
fig.savefig("mwe.png")
Result: