geopandas-projections

name	geopandas-projections
description	Using GeoPandas coordinate projections for accurate distance calculations on geospatial data.

GeoPandas Projections for Distance Calculations

Overview

When calculating distances between geographic features, you must project from geographic coordinates (lat/lon, EPSG:4326) to a projected CRS that preserves distances. Using .distance() on unprojected data gives degrees, not meters/km.

Key Projections

World Azimuthal Equidistant (ESRI:54032)

• Preserves distances from center point
• Good for measuring distances from a single point to boundaries
• Usage: gdf.to_crs("ESRI:54032")

Equal Area Cylindrical (EPSG:6933)

• Preserves area, approximate distances
• Usage: gdf.to_crs("EPSG:6933")

Custom Azimuthal Equidistant

• Best accuracy when measuring from a known center point
• proj_str = f"+proj=aeqd +lat_0={lat} +lon_0={lon} +datum=WGS84 +units=m"

Distance Calculation Pattern

import geopandas as gpd
from shapely.ops import nearest_points

# Load data in WGS84
gdf = gpd.read_file("data.geojson")  # EPSG:4326

# Project to meters-based CRS
gdf_proj = gdf.to_crs("ESRI:54032")

# Calculate distance (returns meters)
dist = gdf_proj.geometry.distance(some_geometry_proj)

# Convert to km
dist_km = dist / 1000

Handling the Antimeridian (Date Line)

The Pacific plate crosses the antimeridian (±180° longitude). Standard projections may split geometries. Solutions:

1. Use a Pacific-centered projection with +lon_0=180 or +lon_0=-160
2. Shift longitudes to 0-360 range before projecting
3. Use azimuthal equidistant centered on Pacific

Point-to-LineString Distance

from shapely.ops import nearest_points

# For a point to a boundary (MultiLineString)
point_proj = earthquake_point.to_crs(proj_crs)
boundary_proj = boundary.to_crs(proj_crs)
distance = point_proj.geometry.distance(boundary_proj.unary_union)