Basemap Heat error / empty map

Question

I am trying to plot a scattered heat map on a defined geo location. I can very well plot a normal scattered map with no background but I want to combine it with a given lat and lon. I get the following empty map.

Input

Input: col[2] and col[3] are the x and y co ordinates & Geo Location Lat:19.997453, Lon:73.789802

000000000023 61.0 19.006113 73.009168 
000000000054 65.0 19.009249 73.000342 
000000000003 19.0 19.001051 73.000080 
000000000012 20.0 19.009390 73.008638 
000000000061 82.0 19.008550 73.003605 
000000000048 86.0 19.006597 73.001057 
00000000005d 60.0 19.003857 73.009618 
000000000006 60.0 19.003370 73.009112 
000000000037 91.0 19.002558 73.000546 
000000000047 32.0 19.006061 73.008239 

Program

from matplotlib import pyplot as plt 
from matplotlib import cm as CM
from matplotlib import mlab as ml
from mpl_toolkits.basemap import Basemap
import numpy as np 

m = Basemap(width=12000000, height=9000000, projection='lcc', 
            resolution='c', lat_0=19.,lon_0=73.)
m.drawcoastlines(linewidth=0.25)

data = np.loadtxt('random_lat_lon_0', unpack=True, 
                  dtype='str, float, float, float')

x  = data[2]
y  = data[3]
z  = data[1]

gridsize = 100 
m.hexbin(x, y, C=z, gridsize=gridsize)

cb = m.colorbar()
#m.set_label('Density')
plt.show()  

No Error But I see only empty map but no scatter plot of data on that.

How to fix ? Thanks !!

Answer 1

I now understand. You are trying to combine answers you received from here-imshow and here-hexbin.

Your problem boils down to the fact that you want to use your Basemap as the "canvas" on which you plot your 2D histogram. But instead of doing that, you are making a Basemap then plotting a 2D histogram separately (using plt.hexbin which makes a separate canvas from your Basemap).

Use m.hexbin and get rid of plt.imshow(). If you really want to use imshow, you will need to make a separately 2D histogram array first, then plot it with imshow. Below is how I would proceed with hexbin.

---

EDIT: Below I randomized some x, y, z data so I could make a plot (and made the coastlines bigger). It's not perfect, but it shows the data plotted.

from matplotlib import pyplot as plt 
from matplotlib import cm as CM
from matplotlib import mlab as ml
from mpl_toolkits.basemap import Basemap
import numpy as np 

m = Basemap(width=12000000, height=9000000, projection='lcc', 
            resolution='c', lat_0=19.,lon_0=73.)
m.drawcoastlines(linewidth=0.25) # I added color='red', lw=2.0

#data = np.loadtxt('inputfile', unpack=True, 
                  dtype='str, int, int, int, int, float')
#
#x  = data[1]
#y  = data[2]
#z  = data[5]
x, y, z = np.random.rand(3, 1000000)
x *= 12e6
y *= 9e6
z *= 20000

gridsize = 100 
m.hexbin(x, y, C=z, gridsize=gridsize, cmap=plt.cm.YlGnBu)

cb = m.colorbar()
m.set_label('Density')
plt.show()