import matplotlib.pyplot as plt
import matplotlib.ticker as mticker
import cartopy.crs as ccrs

from cartopy.mpl.ticker import (LongitudeFormatter, LatitudeFormatter,
                                LatitudeLocator)


ax = plt.axes(projection=ccrs.Mercator())
ax.coastlines()

gl = ax.gridlines(crs=ccrs.PlateCarree(), draw_labels=True,
                  linewidth=2, color='gray', alpha=0.5, linestyle='--')
gl.top_labels = False
gl.left_labels = False
gl.xlines = False
gl.xlocator = mticker.FixedLocator([-180, -45, 0, 45, 180])
gl.ylocator = LatitudeLocator()
gl.xformatter = LongitudeFormatter()
gl.yformatter = LatitudeFormatter()
gl.ylabel_style = {'size': 15, 'color': 'gray'}
gl.xlabel_style = {'color': 'red', 'weight': 'bold'}

plt.show()