geopandas-geospatial

GeoPandas Geospatial Analysis

Overview

GeoPandas extends pandas with spatial operations on geometric types, combining pandas DataFrames with Shapely geometries and Fiona for file I/O. It enables reading, writing, manipulating, and visualizing geospatial vector data (points, lines, polygons) with a familiar pandas-like API.

When to Use

• Reading and writing spatial file formats (Shapefile, GeoJSON, GeoPackage, Parquet)
• Performing spatial joins between geographic datasets (points in polygons, nearest neighbors)
• Running overlay operations (intersection, union, difference, clipping)
• Computing geometric properties (area, distance, buffer, centroid)
• Creating choropleth maps and interactive web maps
• Reprojecting data between coordinate reference systems
• Aggregating spatial features by attribute (dissolve)
• For raster data analysis, use rasterio/xarray instead
• For large-scale distributed geospatial, consider Dask-GeoPandas or Apache Sedona

Prerequisites

pip install geopandas matplotlib
# Optional:
# pip install folium       — interactive maps
# pip install mapclassify  — classification schemes for choropleth
# pip install contextily   — basemaps
# pip install pyarrow      — faster I/O (2-4x speedup)
# pip install psycopg2 geoalchemy2  — PostGIS support

Quick Start

import geopandas as gpd

# Read spatial data
gdf = gpd.read_file("data.geojson")
print(f"Shape: {gdf.shape}, CRS: {gdf.crs}")
print(f"Geometry types: {gdf.geometry.geom_type.unique()}")

# Reproject, compute area, save
gdf_proj = gdf.to_crs("EPSG:3857")
gdf_proj['area_m2'] = gdf_proj.geometry.area
gdf_proj.to_file("output.gpkg")

# Quick map
gdf.plot(column='population', legend=True, figsize=(10, 8))

Core API

1. Data I/O

import geopandas as gpd

# Read various formats
gdf = gpd.read_file("data.shp")           # Shapefile
gdf = gpd.read_file("data.geojson")       # GeoJSON
gdf = gpd.read_file("data.gpkg")          # GeoPackage
gdf = gpd.read_file("data.gpkg", layer="roads")  # Specific layer

# Filtered reading (load only needed data)
gdf = gpd.read_file("data.gpkg", bbox=(xmin, ymin, xmax, ymax))
gdf = gpd.read_file("data.gpkg", columns=["name", "geometry"])
gdf = gpd.read_file("data.gpkg", where="population > 10000")

# Arrow acceleration (2-4x faster)
gdf = gpd.read_file("data.gpkg", use_arrow=True)

# Parquet/Feather (columnar, fast, preserves CRS)
gdf = gpd.read_parquet("data.parquet")
gdf.to_parquet("output.parquet")

# PostGIS database
from sqlalchemy import create_engine
engine = create_engine("postgresql://user:pass@host/db")
gdf = gpd.read_postgis("SELECT * FROM parcels", con=engine, geom_col='geom')
gdf.to_postgis("output_table", con=engine)

# Write
gdf.to_file("output.gpkg")             # GeoPackage (recommended)
gdf.to_file("output.shp")              # Shapefile
gdf.to_file("output.geojson", driver="GeoJSON")

2. CRS Management

# Check current CRS
print(gdf.crs)                  # e.g., EPSG:4326
print(gdf.crs.is_geographic)    # True for lat/lon
print(gdf.crs.is_projected)     # True for meters

# Reproject (transforms coordinates)
gdf_proj = gdf.to_crs("EPSG:3857")       # Web Mercator
gdf_proj = gdf.to_crs(epsg=32633)        # UTM zone 33N

# Set CRS (only when metadata missing, does NOT transform coordinates)
gdf = gdf.set_crs("EPSG:4326")

# Estimate appropriate UTM zone
utm_crs = gdf.estimate_utm_crs()
gdf_utm = gdf.to_crs(utm_crs)

Common EPSG codes:

| Code | Name | Use | |------|------|-----| | 4326 | WGS 84 | GPS coordinates, web data | | 3857 | Web Mercator | Web mapping (Google/OSM tiles) | | 326xx | UTM zones (N) | Area/distance calculations | | 5070 | Albers Equal Area (US) | Area-preserving US maps |

3. Geometric Operations

# Buffer (expand/erode geometry by distance)
buffered = gdf.geometry.buffer(100)      # 100 units (meters if projected)
eroded = gdf.geometry.buffer(-50)        # Negative = erosion

# Simplify (reduce complexity)
simplified = gdf.geometry.simplify(tolerance=10, preserve_topology=True)

# Centroid, convex hull, envelope
centroids = gdf.geometry.centroid
hulls = gdf.geometry.convex_hull
bounds = gdf.geometry.envelope

# Union all geometries
unified = gdf.geometry.union_all()

# Affine transformations
rotated = gdf.geometry.rotate(angle=45, origin='center')
scaled = gdf.geometry.scale(xfact=2.0, yfact=2.0)
translated = gdf.geometry.translate(xoff=100, yoff=50)

# Geometric properties
areas = gdf.geometry.area           # Use projected CRS for accuracy
lengths = gdf.geometry.length       # Perimeter for polygons
is_valid = gdf.geometry.is_valid    # Validate geometry
total = gdf.geometry.total_bounds   # [minx, miny, maxx, maxy]

4. Spatial Analysis

# Spatial join (combine datasets by spatial relationship)
joined = gpd.sjoin(points_gdf, polygons_gdf, predicate='intersects')
joined = gpd.sjoin(gdf1, gdf2, predicate='within')
joined = gpd.sjoin(gdf1, gdf2, predicate='contains', how='left')

# Nearest neighbor join
nearest = gpd.sjoin_nearest(gdf1, gdf2, max_distance=1000, distance_col='dist')

# Overlay operations (set-theoretic)
intersection = gpd.overlay(gdf1, gdf2, how='intersection')
union = gpd.overlay(gdf1, gdf2, how='union')
difference = gpd.overlay(gdf1, gdf2, how='difference')
sym_diff = gpd.overlay(gdf1, gdf2, how='symmetric_difference')

# Dissolve (aggregate by attribute)
dissolved = gdf.dissolve(by='region', aggfunc='sum')
dissolved = gdf.dissolve(by='region', aggfunc={'population': 'sum', 'area': 'mean'})

# Clip to boundary
clipped = gpd.clip(gdf, boundary_gdf)

# Distance calculations (use projected CRS)
distances = gdf.geometry.distance(single_point)

# Spatial predicates
within_mask = gdf1.geometry.within(gdf2.geometry)
intersects_mask = gdf1.geometry.intersects(gdf2.geometry)

5. Visualization

import matplotlib.pyplot as plt

# Basic plot
gdf.plot(figsize=(10, 8))

# Choropleth map
gdf.plot(column='population', cmap='YlOrRd', legend=True, figsize=(12, 8))

# Classification schemes (requires mapclassify)
gdf.plot(column='population', scheme='quantiles', k=5, legend=True)
gdf.plot(column='population', scheme='fisher_jenks', k=5, legend=True)

# Multi-layer map
fig, ax = plt.subplots(figsize=(12, 10))
polygons_gdf.plot(ax=ax, color='lightblue', edgecolor='black')
points_gdf.plot(ax=ax, color='red', markersize=10)
roads_gdf.plot(ax=ax, color='gray', linewidth=0.5)
ax.set_title('Multi-layer Map')
ax.set_axis_off()

# Interactive map (requires folium)
m = gdf.explore(column='population', cmap='YlOrRd', legend=True,
                tooltip=['name', 'population'])
m.save('map.html')

# Multi-layer interactive
m = gdf1.explore(color='blue', name='Layer 1')
gdf2.explore(m=m, color='red', name='Layer 2')
import folium
folium.LayerControl().add_to(m)

# Basemap (requires contextily)
import contextily as ctx
gdf_wm = gdf.to_crs(epsg=3857)
ax = gdf_wm.plot(alpha=0.5, figsize=(10, 10))
ctx.add_basemap(ax)

Key Concepts

Data Structures

• GeoSeries: Pandas Series of Shapely geometries with spatial methods (area, distance, buffer, etc.)
• GeoDataFrame: Pandas DataFrame with one or more geometry columns. One column is the "active geometry" used by spatial methods

from shapely.geometry import Point

# Create from coordinates
gdf = gpd.GeoDataFrame(
    {'name': ['A', 'B'], 'value': [10, 20]},
    geometry=[Point(0, 0), Point(1, 1)],
    crs="EPSG:4326"
)

# Multiple geometry columns
gdf['centroid'] = gdf.geometry.centroid
gdf = gdf.set_geometry('centroid')  # Switch active geometry

CRS Rules for Spatial Operations

• Always check CRS before any spatial operation: print(gdf.crs)
• Match CRS before spatial joins, overlays, or distance calculations
• Use projected CRS (meters) for area/distance — geographic CRS (degrees) gives wrong results
• set_crs() only adds metadata; to_crs() transforms coordinates

Spatial Indexing

GeoPandas