I don't think surface curvature will be helpful understand the differences between two EM maps. But I was curious what it would look like. So here's a Python script and an image on a simulated map at 15 Angstroms. You use the script by opening your map, selecting the surface (ctrl-click on it), then open the curvature.py script (menu File / Open…). Here's a description of the method it uses from the comments at the top of the curvature.py file.
# Color selected surface pieces by mean curvature.
#
# Gray at the average curvature value over the surface, and blue and red
# at +/- 3 standard deviations of curvature values across the surface.
#
# The curvature is estimated from the vertices and normals of the triangulated
# surface in simple way which will show artifacts from non-isotropic meshes.
# For each triangle edge it computes the normal vector rotation from one vertex
# to the other divided by the edge length. The vertex mean curvature is the
# mean of the curvatures computed for each edge.
#