Creating a human density map

I had originally planned on producing a worldwide human density map, but the graphics available don't allow for setting the color of each country. So, I built a density map for the United States.

The algorithm is:

1. Obtain graphic shapes for each of the states.
2. Obtain the density for each state.
3. Decide on a color range and apply the lowest density to one end of the range and the highest to the other end.
4. For each state:
   • Determine it's density
   • Lookup that density value in the range and select a color
   • Draw the state

This is coded with the following (comments embedded as the code proceeds):

%matplotlib inline
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
from matplotlib.patches import Polygon
import pandas as pd
import numpy as np
import matplotlib
# create the map
map = Basemap(llcrnrlon=-119,llcrnrlat=22,urcrnrlon=-64,urcrnrlat=49,
        projection='lcc',lat_1=33,lat_2=45,lon_0=-95)
# load the shapefile, use the name 'states'
# download from https...