Choropleth map not showing anything but empty map

I tried to plot the Choropleth map from folium but its not showing the gradient colours for different boroughs of london

shapefile link(used ‘statistical-gis-boundaries-london.zip’ ): https://data.london.gov.uk/dataset/statistical-gis-boundary-files-london

csv data( used ‘london-borough-profiles.csv’ ): https://data.london.gov.uk/dataset/london-borough-profiles

I used the chropleth geojson data from the above shapefile which I converted to geojson through a code I stumbled upon online.

import shapefile
# read the shapefile
fïlepath = "statistical-gis-boundaries-london/ESRI/London_Borough_Excluding_MHW.shp"
reader = shapefile.Reader(fïlepath)
fields = reader.fields[1:]
field_names = [field[0] for field in fields]
buffer = []
for sr in reader.shapeRecords():
   atr = dict(zip(field_names, sr.record))
   geom = sr.shape.__geo_interface__
   buffer.append(dict(type="Feature", \
    geometry=geom, properties=atr)) 

# write the GeoJSON file
from json import dumps
geojson = open("london-borough.json", "w")
geojson.write(dumps({"type": "FeatureCollection",\
"features": buffer}, indent=2) + "\n")
geojson.close()

I made sure that the “on_key” value and a column in columns are same(same data)

done data cleaning:

state_data = pd.read_csv("london-borough-profiles.csv")
state_data = state_data[['Area_name', 'Population_density_(per_hectare)_2017']]
state_data['Population_density_(per_hectare)_2017'] = state_data['Population_density_(per_hectare)_2017'].replace(".",np.nan)
state_data['Population_density_(per_hectare)_2017'] = state_data['Population_density_(per_hectare)_2017'].astype(float)
state_data = state_data.dropna()
I think this might be because of the geojson data.

Any help will be appreciated. code:

m = folium.Map(location=[51.5074, -0.1278], zoom_start=10)
london_geo = "london-borough.json"
folium.Choropleth(
    geo_data=london_geo,
    name='choropleth',
    data=state_data,
    columns=['Area_name', 'Population_density_(per_hectare)_2017'],
    key_on='feature.properties.NAME',
    fill_color='YlGn',
    fill_opacity=0.7,
    line_opacity=0.2,
    legend_name='Population_density_(per_hectare)_2017'
).add_to(m)

folium.LayerControl().add_to(m)

m

No error messages, just the map is showing up with no color gradient for the boroughs

folium version : - 0.8.3

[loramf]

@drkrthnblk I have found the solution to your problem. The reason why the chloropath does not show up on the map is not to do with the key_on but the coordinates in the JSON file. The beginning of the JSON file, “london-borough.json”, looks like this:

{“type”: “FeatureCollection”, “crs”: { “type”: “name”, “properties”: [{ “name”: “urn:ogc:def:crs:OGC:1.3:CRS84” } }, “features”: [{ “type”: “Feature”, “properties”: { “NAME”: “Kingston upon Thames”, “GSS_CODE”: “E09000021”, “HECTARES”: 3726.117, “NONLD_AREA”: 0.0, “ONS_INNER”: “F”, “SUB_2009”: “”,“SUB_2006”: “” }, “geometry”: { “type”: “Polygon”, “coordinates”: [ [ [ 516401.6, 160201.8 ], [ 516407.3, 160210.5 ], [ 516413.3, 160217.4 ], …

As you can see all the coordinates are extremely large, whereas on the Folium map London should be around [50, -0.25]. This is because the shapefile coordinates were stored under a different coordinate system to the Folium map, whose system is called EPSG 4326.

By projecting the coordinates onto the correct system the chloropleth will show up on the map. Here is my code for doing this (note that you can import the shapefile directly using geopandas):

import geopandas as gpd data_source = 'data/statistical-gis-boundaries-london/ESRI/London_Borough_Excluding_MHW.shp' data = gpd.read_file(fp) Now project coordinates to EPSG 4326: data['geometry'] = data['geometry'].to_crs(epsg=4326) data.to_file("london-borough.json", driver="GeoJSON")

Now if you look at “london-borough.json” you’ll see that the first few coordinates are as such: [ [ -0.329102847925613, 51.328483175466303 ], [ -0.329018221029286, 51.328560212318934 ], [ -0.32892987768375, 51.328621007587756 ], …

To check the London boroughs can now be plotted on the Folium map you can run the following code: m = folium.Map(location = [51.505453, -0.268839]) 'folium.GeoJson('data/london-borough.json').add_to(m) m

and you should be able to plot the chloropleth: m = folium.Map(location = [51.505453, -0.268839]) folium.Choropleth( geo_data='data/london-borough.json', name='choropleth', data= .........., columns= .........., key_on= .........., fill_color='YlGn', fill_opacity=0.7, line_opacity=0.2 ).add_to(m) m Note that ‘folium.Chloropleth’ is used instead of ‘.choropleth’ which is now deprecated. Also, I am using Jupyter Notebook - this did not work on Google Chrome so I had to switch to Firefox.

[Conengmo]

Thanks for the help on this @loramf! I’m closing the issue.