python - In scipy's ConvexHull, what does "area" measure?

Question

The value of the "area" attribute in scipy ConvexHull (see http://docs.scipy.org/doc/scipy/reference/generated/scipy.spatial.ConvexHull.html) object does not seem to be (what I understand to be) the area of the convex hull. On the other hand, the value of "volume" does seem to be the area of the convex hull.

from scipy.spatial import ConvexHull
import numpy

points = numpy.array([[-1,-1], [1,1], [-1, 1], [1,-1]])
hull = ConvexHull(points)

print("Volume is %2.2f" % hull.volume) # Prints 4.00
print("Area is %2.2f" % hull.area) # Prints 8.00

In the above example, I expect the area of the convex hull of the 4 points to be 4.0. That's what the "volume" is. What then does "area" give us?

Answer 1

Volume and area are 3d concepts, but your data is 2d - a 2x2 square. Its area is 4, and perimeter is 8 (the 2d counterparts).