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import os
import folium

print(folium.__version__)

Using `folium.colormap`

A few examples of how to use folium.colormap in choropleths.

Let's load a GeoJSON file, and try to choropleth it.



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import json
import pandas as pd

us_states = os.path.join('data', 'us-states.json')
US_Unemployment_Oct2012 = os.path.join('data', 'US_Unemployment_Oct2012.csv')

geo_json_data = json.load(open(us_states))
unemployment = pd.read_csv(US_Unemployment_Oct2012)

unemployment_dict = unemployment.set_index('State')['Unemployment']









    




IOErrorTraceback (most recent call last)
<ipython-input-2-0e1e9a7e1804> in <module>()
      5 US_Unemployment_Oct2012 = os.path.join('data', 'US_Unemployment_Oct2012.csv')
      6 
----> 7 geo_json_data = json.load(open(us_states))
      8 unemployment = pd.read_csv(US_Unemployment_Oct2012)
      9 

IOError: [Errno 2] No such file or directory: 'data\\us-states.json'

Self-defined

You can build a choropleth in using a self-defined function. It has to output an hexadecimal color string of the form #RRGGBB or #RRGGBBAA.



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def my_color_function(feature):
    """Maps low values to green and hugh values to red."""
    if unemployment_dict[feature['id']] > 6.5:
        return '#ff0000'
    else:
        return '#008000'



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m = folium.Map([43, -100], tiles='cartodbpositron', zoom_start=4)

folium.GeoJson(
    geo_json_data,
    style_function=lambda feature: {
        'fillColor': my_color_function(feature),
        'color': 'black',
        'weight': 2,
        'dashArray': '5, 5'
    }
).add_to(m)

m.save(os.path.join('results', 'Colormaps_0.html'))

m

StepColormap

But to help you define you colormap, we've embedded StepColormap in folium.colormap.

You can simply define the colors you want, and the index (thresholds) that correspond.



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import branca.colormap as cm


step = cm.StepColormap(['green', 'yellow', 'red'],
                       vmin=3, vmax=10, index=[3, 4, 8, 10],
                       caption='step')

step



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m = folium.Map([43, -100], tiles='cartodbpositron', zoom_start=4)

folium.GeoJson(
    geo_json_data,
    style_function=lambda feature: {
        'fillColor': step(unemployment_dict[feature['id']]),
        'color': 'black',
        'weight': 2,
        'dashArray': '5, 5'
    }
).add_to(m)

m.save(os.path.join('results', 'Colormaps_1.html'))

m

If you specify no index, colors will be set uniformely.



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cm.StepColormap(['r', 'y', 'g', 'c', 'b', 'm'])

LinearColormap

But sometimes, you would prefer to have a continuous set of colors. This can be done by LinearColormap.



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linear = cm.LinearColormap(['green', 'yellow', 'red'],
                           vmin=3, vmax=10)

linear



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m = folium.Map([43, -100], tiles='cartodbpositron', zoom_start=4)

folium.GeoJson(
    geo_json_data,
    style_function=lambda feature: {
        'fillColor': linear(unemployment_dict[feature['id']]),
        'color': 'black',
        'weight': 2,
        'dashArray': '5, 5'
    }
).add_to(m)

m.save(os.path.join('results', 'Colormaps_2.html'))

m

Again, you can set the index if you want something irregular.



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cm.LinearColormap(['red', 'orange', 'yellow', 'green'],
                  index=[0, 0.1, 0.9, 1.0])

If you want to transform a linear map into a step one, you can use the method to_step.



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linear.to_step(6)

You can also use more sophisticated rules to create the thresholds.



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linear.to_step(
    n=6,
    data=[30.6, 50, 51, 52, 53, 54, 55, 60, 70, 100],
    method='quantiles',
    round_method='int'
)

And the opposite is also possible with to_linear.



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step.to_linear()

Build-in

For convenience, we provide a (small) set of built-in linear colormaps, in folium.colormap.linear.



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cm.linear.OrRd

You can also use them to generate regular StepColormap.



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cm.linear.PuBu.to_step(12)

Of course, you may need to scale the colormaps to your bounds. This is doable with .scale.



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cm.linear.YlGn.scale(3, 12)



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cm.linear.RdGy.to_step(10).scale(5, 100)

At last, if you want to check them all, simply ask for linear in the notebook.



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cm.linear

Draw a `ColorMap` on a map

By the way, a ColorMap is also a Folium Element that you can draw on a map.



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m = folium.Map(tiles='cartodbpositron')

colormap = cm.linear.Set1.scale(0, 35).to_step(10)
colormap.caption = 'A colormap caption'
m.add_child(colormap)

#m.save(os.path.join('results', 'Colormaps_3.html'))

m



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