from cartopy.mpl.ticker import LatitudeFormatter, LongitudeFormatter

fig = plt.figure()
ax = fig.add_subplot(111, projection=ccrs.Miller())
ax.set_global()
ax.coastlines()
ax.gridlines()
ax.set_xticks(np.linspace(-180, 180, 7), crs=ccrs.PlateCarree())
ax.set_yticks(np.linspace(-90, 90, 7), crs=ccrs.PlateCarree())
lon_formatter = LongitudeFormatter()
lat_formatter = LatitudeFormatter()
ax.xaxis.set_major_formatter(lon_formatter)
ax.yaxis.set_major_formatter(lat_formatter)
ax.tick_params('both', length=0)