`folium.GeoJson` displays all polygons in GeoDataframe but not individual ones

Question

folium.GeoJson displays all the counties of New York State:

import geopandas as gpd
gdf = gpd.read_file("Counties_Shoreline.shp")
m = folium.Map(location=[43.062776, -75.420884], tiles="cartodbpositron", zoom_start=7)
folium.GeoJson(data=gdf["geometry"]).add_to(m)
m

However, it fails to display a single county, outputting a map without borders when only the first row data, gdf["geometry"][0], is used:

m = folium.Map(location=[43.062776, -75.420884], tiles='cartodbpositron', zoom_start=7)
folium.GeoJson(data=gdf["geometry"][0]).add_to(m)
m

This despite the fact that the polygon appears fine, rendering inside Jupyter Notebook.

Data here: http://gis.ny.gov/gisdata/fileserver/?DSID=927&file=NYS_Civil_Boundaries.shp.zip Shapefile: Counties_Shoreline.shp

Answer 1

Because gdf["geometry"]) is a GeoSerie and gdf["geometry"][0] is a shapely geometry (the geometry column is a list of shapely geometries).

The type of data

data=gdf["geometry"]
print(type(data)) 
<class 'geopandas.geoseries.GeoSeries'>
data= gdf["geometry"][0]
print(data)
<class 'shapely.geometry.polygon.Polygon'>

The GeoDataFrame has a projection

print(gdf.crs)
epsg:26918

but the shapely geometry not and Impossible to draw GeoJSON that has crs other than 4326

A solution is to change de projection of the GeoDataFrame to EPSG:4326 (WSG84)

gdf = gdf.to_crs("EPSG:4326") 
print(gdf.crs)
EPSG:4326
m = folium.Map(location=[43.062776, -75.420884],tiles="cartodbpositron", zoom_start=7)
folium.GeoJson(data=gdf["geometry"]).add_to(m) 
m

And

m = folium.Map(location=[43.062776, -75.420884], tiles='cartodbpositron', zoom_start=7)
folium.GeoJson(data=gdf["geometry"][0]).add_to(m)
m