Matplotlib EPA AQI cmap

aqicmap.py

import matplotlib.pyplot as plt
import matplotlib.colors as mc
import numpy as np
pmedges = np.asarray([0.0, 12.1, 35.5, 55.5, 150.5, 250.5, 500.5])
o8edges = np.asarray([0.0, 55, 71, 86, 106, 201, 500.])
o1edges = np.asarray([0.0, 60, 125,165,205, 405, 604.])

aqicolors = ['#00e400', '#ffff00', '#ff7e00', '#ff0000', '#8f3f97', '#7e0023']
colors = ['grey'] + aqicolors + ['k']

pmcmap, pmnorm = mc.from_levels_and_colors(pmedges, colors, extend='both')
o8cmap, o8norm = mc.from_levels_and_colors(o8edges, colors, extend='both')

testz = np.array([
    [-1e6, -1e3, -1],
    [0, 6, 12],
    [12.1, 25, 35.4],
    [35.5, 40, 55.4],
    [55.5, 100, 150.4],
    [150.5, 200, 250.4],
    [250.5, 350, 500.4],
    [500.5, 1e3, 1e5],
])
qm = plt.pcolormesh(testz, cmap=pmcmap, norm=pmnorm)
cbar = plt.colorbar(qm, ticks=(pmedges[:-1] + pmedges[1:])/2, orientation='horizontal')
cbar.ax.set_xticklabels(['Good', 'Moderate', 'USG', 'Unhealthy', 'Very U', 'Hazardous'])

The code above produces the figure below. Note that there three columns of identical color, which makes the rows look like stripes.