python - Display heat map on a Matplotlib/Basemap

问题

I have a dataset of longitudes/latitudes as follows:

id,spp,lon,lat
1a,sp1,1,9
1b,sp1,3,11
1c,sp1,6,12
2a,sp2,1,9
2b,sp2,1,10
2c,sp2,3,10
2d,sp2,4,11
2e,sp2,5,12
2f,sp2,6,12
3a,sp3,4,13
3b,sp3,5,11
3c,sp3,8,8
4a,sp4,4,12
4b,sp4,6,11
4c,sp4,7,8
5a,sp5,8,8
5b,sp5,7,6
5c,sp5,8,2
6a,sp6,8,8
6b,sp6,7,5
6c,sp6,8,3

I want to display a heat map representing the density of points over a geographical map using Matplotlib/Basemap, using the code below (more or less based on this one):

from mpl_toolkits.basemap import Basemap
from matplotlib import cm as cmap
import matplotlib.pyplot as plt
import numpy as np
import warnings

warnings.filterwarnings("ignore")

# input data
coords = np.loadtxt("testdata.csv", delimiter=',', skiprows=1, usecols=(2, 3))
lon = coords[:,0]
lat = coords[:,1]

# create map
m = Basemap(width=12000000, height=9000000, projection='lcc',
            resolution='c', lat_0=6, lon_0=4.)
m.drawcoastlines(linewidth=0.25)

# create heatmap
heatmap, xedges, yedges = np.histogram2d(lon, lat, bins=20)

# plot map
##plt.clf()
m.imshow(heatmap.T, interpolation='none', cmap=cmap.jet)
plt.show()

However, the heat map is displayed but the map is not shown (see attached figure)

This looks the opposite of this question, in which the map is displayed but not the heat map (however that solution was not very helpful to me).

Any hints?

来源：https://stackoverflow.com/questions/46555175/python-display-heat-map-on-a-matplotlib-basemap