How to get higher resolution in topography map

Question

I need to make a topographical map, but so far the resolution is not high enough with 'resolution=f'. Is there better way to make higher resolution? Appreciate that in advance.

import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
import pandas as pd

minlon = -95
maxlon = -91
minlat = 17
maxlat = 20

fig, ax = plt.subplots(figsize=(15, 12))
m = Basemap(projection='cyl', resolution='f', llcrnrlat=minlat, urcrnrlat=maxlat, llcrnrlon=minlon, urcrnrlon=maxlon)

m.etopo()

m.drawcoastlines(linewidth=0.2)