run2-geopandas-spatial-joins

name	run2_geopandas_spatial_joins
description	Improved guide for performing spatial joins with GeoPandas, specifically handling antimeridian crossing polygons like the Pacific Plate.

Spatial Joins and Antimeridian in GeoPandas

GeoPandas provides sjoin to join points and polygons based on their spatial relationship.

Pacific Plate and the Antimeridian

The Pacific Plate spans across the 180° meridian (antimeridian). Standard WGS84 (EPSG:4326) coordinates wrap around this line. High-quality datasets like PB2002 split tectonic plates that cross the antimeridian into MultiPolygon geometries. This means a standard spatial join using Euclidean intersection rules on EPSG:4326 will correctly identify points within the plate without false positives connecting -180 and 180 through Greenwich.

Usage

import geopandas as gpd

# Load points and polygons
points = gpd.read_file('points.geojson')
polygons = gpd.read_file('polygons.geojson')

# Ensure matching CRS before spatial join
if points.crs != polygons.crs:
    points = points.to_crs(polygons.crs)

# Filter polygons (e.g. Code == 'PA' for Pacific Plate)
pacific_plate = polygons[polygons['Code'] == 'PA']

# Find points within the polygon
points_in_poly = gpd.sjoin(points, pacific_plate, predicate='within')

print(f"Points inside PA plate: {len(points_in_poly)}")