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Plotting polygons with Folium

This example demonstrates how to plot polygons on a Folium map.

[1]:
import geopandas as gpd
import folium
import matplotlib.pyplot as plt

Load geometries

This example uses the nybb dataset, which contains polygons of New York boroughs.

[2]:
path = gpd.datasets.get_path('nybb')
df = gpd.read_file(path)
df.head()
[2]:
BoroCode BoroName Shape_Leng Shape_Area geometry
0 5 Staten Island 330470.010332 1.623820e+09 MULTIPOLYGON (((970217.022 145643.332, 970227....
1 4 Queens 896344.047763 3.045213e+09 MULTIPOLYGON (((1029606.077 156073.814, 102957...
2 3 Brooklyn 741080.523166 1.937479e+09 MULTIPOLYGON (((1021176.479 151374.797, 102100...
3 1 Manhattan 359299.096471 6.364715e+08 MULTIPOLYGON (((981219.056 188655.316, 980940....
4 2 Bronx 464392.991824 1.186925e+09 MULTIPOLYGON (((1012821.806 229228.265, 101278...

Plot from the original dataset

[3]:
df.plot(figsize=(6, 6))
plt.show()
../_images/gallery_polygon_plotting_with_folium_5_0.png

Notice that the values of the polygon geometries do not directly represent the values of latitude of longitude in a geographic coordinate system. To view the coordinate reference system of the geometry column, access the crs attribute:

[4]:
df.crs
[4]:
<Projected CRS: EPSG:2263>
Name: NAD83 / New York Long Island (ftUS)
Axis Info [cartesian]:
- X[east]: Easting (US survey foot)
- Y[north]: Northing (US survey foot)
Area of Use:
- name: United States (USA) - New York - counties of Bronx; Kings; Nassau; New York; Queens; Richmond; Suffolk.
- bounds: (-74.26, 40.47, -71.8, 41.3)
Coordinate Operation:
- name: SPCS83 New York Long Island zone (US Survey feet)
- method: Lambert Conic Conformal (2SP)
Datum: North American Datum 1983
- Ellipsoid: GRS 1980
- Prime Meridian: Greenwich

The epsg:2263 crs is a projected coordinate refererence system with linear units (ft in this case). As folium (i.e. leaflet.js) by default accepts values of latitude and longitude (angular units) as input, we need to project the geometry to a geographic coordinate system first.

[5]:
# Use WGS 84 (epsg:4326) as the geographic coordinate system
df = df.to_crs(epsg=4326)
print(df.crs)
df.head()
epsg:4326
[5]:
BoroCode BoroName Shape_Leng Shape_Area geometry
0 5 Staten Island 330470.010332 1.623820e+09 MULTIPOLYGON (((-74.05051 40.56642, -74.05047 ...
1 4 Queens 896344.047763 3.045213e+09 MULTIPOLYGON (((-73.83668 40.59495, -73.83678 ...
2 3 Brooklyn 741080.523166 1.937479e+09 MULTIPOLYGON (((-73.86706 40.58209, -73.86769 ...
3 1 Manhattan 359299.096471 6.364715e+08 MULTIPOLYGON (((-74.01093 40.68449, -74.01193 ...
4 2 Bronx 464392.991824 1.186925e+09 MULTIPOLYGON (((-73.89681 40.79581, -73.89694 ...
[6]:
df.plot(figsize=(6, 6))
plt.show()
../_images/gallery_polygon_plotting_with_folium_10_0.png

Create Folium map

[7]:
m = folium.Map(location=[40.70, -73.94], zoom_start=10, tiles='CartoDB positron')
m
[7]:
Make this Notebook Trusted to load map: File -> Trust Notebook

Add polygons to map

Overlay the boundaries of boroughs on map with borough name as popup:

[8]:
for _, r in df.iterrows():
    # Without simplifying the representation of each borough,
    # the map might not be displayed
    sim_geo = gpd.GeoSeries(r['geometry']).simplify(tolerance=0.001)
    geo_j = sim_geo.to_json()
    geo_j = folium.GeoJson(data=geo_j,
                           style_function=lambda x: {'fillColor': 'orange'})
    folium.Popup(r['BoroName']).add_to(geo_j)
    geo_j.add_to(m)
m
[8]:
Make this Notebook Trusted to load map: File -> Trust Notebook

Add centroid markers

In order to properly compute geometric properties, in this case centroids, of the geometries, we need to project the data to a projected coordinate system.

[9]:
# Project to NAD83 projected crs
df = df.to_crs(epsg=2263)

# Access the centroid attribute of each polygon
df['centroid'] = df.centroid

Since we’re again adding a new geometry to the Folium map, we need to project the geometry back to a geographic coordinate system with latitude and longitude values.

[10]:
# Project to WGS84 geographic crs

# geometry (active) column
df = df.to_crs(epsg=4326)

# Centroid column
df['centroid'] = df['centroid'].to_crs(epsg=4326)

df.head()
[10]:
BoroCode BoroName Shape_Leng Shape_Area geometry centroid
0 5 Staten Island 330470.010332 1.623820e+09 MULTIPOLYGON (((-74.05051 40.56642, -74.05047 ... POINT (-74.15340 40.58085)
1 4 Queens 896344.047763 3.045213e+09 MULTIPOLYGON (((-73.83668 40.59495, -73.83678 ... POINT (-73.81847 40.70757)
2 3 Brooklyn 741080.523166 1.937479e+09 MULTIPOLYGON (((-73.86706 40.58209, -73.86769 ... POINT (-73.94768 40.64472)
3 1 Manhattan 359299.096471 6.364715e+08 MULTIPOLYGON (((-74.01093 40.68449, -74.01193 ... POINT (-73.96719 40.77725)
4 2 Bronx 464392.991824 1.186925e+09 MULTIPOLYGON (((-73.89681 40.79581, -73.89694 ... POINT (-73.86653 40.85262)
[11]:
for _, r in df.iterrows():
    lat = r['centroid'].y
    lon = r['centroid'].x
    folium.Marker(location=[lat, lon],
                  popup='length: {} <br> area: {}'.format(r['Shape_Leng'], r['Shape_Area'])).add_to(m)

m
[11]:
Make this Notebook Trusted to load map: File -> Trust Notebook