surface.py

#!pip install area
from area import area
from functools import partial

def make_polygon(coords, size):
    left_long, bottom_lat = coords
    return np.array([[[left_long, bottom_lat],
                      [left_long, bottom_lat + size],
                      [left_long + size, bottom_lat + size],
                      [left_long + size, bottom_lat],
                      [left_long, bottom_lat]]], dtype=np.float32)

def surface_polygons(grid_size=5):
    long, lat = np.meshgrid(np.arange(-180, 180, grid_size), 
                            np.arange(90-grid_size, -90-grid_size, -grid_size))
    coords = np.dstack([long, lat])
    polygons = np.apply_along_axis(func1d=partial(make_polygon, size=grid_size), 
                                   axis=2, arr=coords)
    return polygons

def surface_area(polygons, perc=True):
    meridian_surface_area = np.array(list(map(area, 
                            map(lambda c: {'type': 'Polygon', 'coordinates': c.tolist()}, 
                            polygons[:, 0]))))/1e6
    surface_area = np.tile(meridian_surface_area.reshape(-1, 1), polygons.shape[1])
    surface_perc = (surface_area / surface_area.sum())
    return surface_perc if perc else surface_area