How Can I Classify Points Under Sub-Regions on a Map in GeoPandas?

I have a map in geopandas and have overlayed it with a scatterplot of events:

The shape file breaks the geography into sub-regions (as shown in the picture above). However, the scatter plot points do not have information on the subregions to which they belong. I want to use the coordinates to assign the name of the subregion to the pandas row of the event. How could I go about this please? I suspect I need to use a for loop of some kind, but I'm not sure how to check if a point lies within a specific polygon.

Solution

Use Spatial Join:

A common use case might be a spatial join between a point layer and a polygon layer where you want to retain the point geometries and grab the attributes of the intersecting polygons.

import geopandas as gpd
region = gpd.read_file(r"/home/bera/Desktop/GIStest/regions.geojson")
# region.head(1)
#    id Region                                           geometry
# 0  15      A  POLYGON ((481571.645 7195961.743, 487345.148 7..

point = gpd.read_file(r"/home/bera/Desktop/GIStest/regionpoints.geojson")

# point.head()
#    id                        geometry
# 0   0  POINT (529586.940 7163711.300)
# 1   1  POINT (505472.742 7192060.117)
# 2   2  POINT (493737.417 7209323.959)
# 3   3  POINT (489694.110 7172779.451)
# 4   4  POINT (540742.212 7170046.145)

#I only want to join the Region column to the points
sj = gpd.sjoin(left_df=point, right_df=region[["Region", "geometry"]], how="left", predicate="intersects")
sj = sj.drop(columns=["index_right"])

#sj.head()
#    id                        geometry Region
# 0   0  POINT (529586.940 7163711.300)    NaN
# 1   1  POINT (505472.742 7192060.117)      D
# 2   2  POINT (493737.417 7209323.959)    NaN
# 3   3  POINT (489694.110 7172779.451)      B
# 4   4  POINT (540742.212 7170046.145)    NaN

#Not all points are within a Region, they get NaN: