title: Colormap/color problems with bar3d plot
body: <p>I have written some code to plot the longitude and latitude of towns/cities in the UK with the 3D bar height representing the population of these places. I am trying to also colour code the bars using a colormap so that the variation in population can be more easily seen. However, my code doesnt seem to follow the colormap and instead all the bars have very similar colours - I am not sure where I have gone wrong</p>
  
  <pre><code>from mpl_toolkits.mplot3d import Axes3D
  import matplotlib.pyplot as plt
  import numpy as np
  
  pop = [189120, 91297, 107123, 107355, 94782, 87590, 142968, 1085810, 117963, 147663, 194189, 187503, 349561, 229700, 535907, 145818, 335145, 110507, 116447, 86011, 88483, 119441, 325949, 106943, 92363, 255394, 109805, 144170, 109185, 468720, 113507, 120046, 104157, 589900, 136362, 88243, 88134, 88855, 91053, 94932, 120256, 162949, 284321, 144957, 474632, 443760, 100160, 552267, 8173941, 211228, 107627, 510746, 174700, 171750, 268064, 128060, 215173, 186682, 289301, 86552, 96555, 159994, 161707, 234982, 154718, 238137, 97886, 95580, 218705, 107926, 109691, 134022, 103886, 518090, 155298, 123187, 253651, 175547, 91703, 102885, 89663, 105878, 270726, 174286, 109015, 179485, 182441, 142723, 99251, 165456, 131982, 91930, 218791, 83641, 103608, 105367, 265178, 100153, 109120, 152841]
  
  lat = [57.14369, 53.55, 51.56844, 51.26249, 51.37795, 52.13459, 53.39337, 52.48142, 53.75, 53.81667, 53.58333, 50.72048, 53.79391, 50.82838, 51.45523, 52.2, 51.48, 51.73575, 51.9, 53.1905, 53.25, 51.88921, 52.40656, 51.11303, 54.52429, 52.92277, 53.52327, 56.5, 50.76871, 55.95206, 50.7236, 54.96209, 51.38914, 55.86515, 51.86568, 53.56539, 53.71667, 54.68611, 50.85519, 51.75369, 51.62907, 53.64904, 53.7446, 52.05917, 53.79648, 52.6386, 53.22683, 53.41058, 51.50853, 51.87967, 51.26667, 53.48095, 54.57623, 52.04172, 54.97328, 51.58774, 52.25, 52.62783, 52.9536, 52.52323, 53.54051, 51.75222, 52.57364, 50.37153, 50.71667, 50.79899, 53.76667, 51.58571, 51.45625, 53.61766, 53.43012, 53.42519, 53.48771, 53.38297, 51.50949, 52.41426, 50.90395, 51.53782, 53.64779, 53.45, 51.90224, 53.40979, 53.00415, 54.90465, 52.56667, 51.62079, 51.55797, 52.67659, 53.68331, 53.39254, 51.65531, 52.51868, 51.50853, 51.34603, 53.53333, 51.31903, 52.58547, 52.18935, 50.81448, 53.95763]
  
  long = [-2.09814, -1.48333, 0.45782, -1.08708, -2.35907, -0.46632, -3.01479, -1.89983, -2.48333, -3.05, -2.43333, -1.8795, -1.75206, -0.13947, -2.59665, 0.11667, -3.18, 0.46958, -2.08333, -2.89189, -1.41667, 0.90421, -1.51217, -0.18312, -1.55039, -1.47663, -1.13691, -2.96667, 0.28453, -3.19648, -3.52751, -1.60168, 0.54863, -4.25763, -2.2431, -0.07553, -1.85, -1.2125, 0.57292, -0.47517, -0.74934, -1.78416, -0.33525, 1.15545, -1.54785, -1.13169, -0.53792, -2.97794, -0.12574, -0.41748, 0.51667, -2.23743, -1.23483, -0.75583, -1.61396, -2.99835, -0.88333, 1.29834, -1.15047, -1.46523, -2.1183, -1.25596, -0.24777, -4.14305, -2.0, -1.09125, -2.71667, 0.60459, -0.97113, -2.1552, -1.35678, -2.32443, -2.29042, -1.4659, -0.59541, -1.78094, -1.40428, 0.71433, -3.00648, -2.73333, -0.20256, -2.15761, -2.18538, -1.38222, -1.81667, -3.94323, -1.78116, -2.44926, -1.49768, -2.58024, -0.39602, -1.9945, -0.12574, -2.97665, -2.61667, -0.55893, -2.12296, -2.22001, -0.37126, -1.08271]
  
  
  fig = plt.figure()
  ax = Axes3D(fig)
  
  X,Y,Z = np.array(long),np.array(lat),np.log10(np.array(pop))
  
  colours = plt.cm.rainbow_r(Z/np.log10(max(pop)))
  
  plot1 = ax.bar3d(X,Y,Z,dx=0.2,dy=0.2,dz=Z/3,color=colours)
  ax.set_xlabel('\nLongitude (\u00B0)')
  ax.set_ylabel('\nLatitude (\u00B0)')
  ax.set_zlabel('\nlog\u2081\u2080(Population)')
  ax.set_zlim3d(4,7)
  ax.view_init(elev=70,azim=280)
  
  
  colourMap = plt.cm.ScalarMappable(cmap=plt.cm.rainbow_r)
  colourMap.set_array(Z)
  colBar = plt.colorbar(colourMap).set_label('log\u2081\u2080(Population)')
  
  plt.show()
  </code></pre>
  
  <p>The code produces this plot:<br>
  <img src="https://i.stack.imgur.com/PeljD.png" alt="plot"></p>
  
  <p>I think that the majority of the bars should be red/orange in colour, with only the major cities being yellow/green/blue...</p>