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GeoParquet Best Practices

This guide explains the optimizations that make GeoParquet files fast and efficient for spatial queries.

Quick Checklist

Run gpio check all myfile.parquet to verify your file follows these best practices:

  • [ ] Spatial ordering (Hilbert curve)
  • [ ] Bbox column with covering metadata
  • [ ] ZSTD compression
  • [ ] Appropriate row group sizes

Spatial Ordering

What It Is

Spatial ordering arranges rows so that geographically nearby features are stored together in the file. gpio uses Hilbert curve ordering, which maps 2D space to 1D while preserving locality.

Why It Matters

Without spatial ordering: 

Row 1: New York
Row 2: Tokyo
Row 3: London
Row 4: Sydney
...

With Hilbert ordering: 

Row 1: New York
Row 2: Boston
Row 3: Philadelphia
Row 4: Washington DC
...

Benefits: - Spatial queries read fewer row groups - Better compression (similar coordinates compress well) - Reduced I/O for bounding box filters

How to Apply

# Sort existing file
gpio sort hilbert input.parquet sorted.parquet

# Convert with automatic Hilbert ordering (default)
gpio convert input.shp output.parquet

# Convert without Hilbert ordering (faster but less optimal)
gpio convert input.shp output.parquet --skip-hilbert

Bounding Box Columns

What They Are

A bbox column stores the bounding box for each feature as a struct:

bbox: {xmin: -122.5, ymin: 37.5, xmax: -122.0, ymax: 38.0}

Why They Matter

Spatial queries typically need to check "does this feature intersect my area of interest?"

Without bbox: Must decode WKB geometry and compute intersection (slow) With bbox: Compare 4 numbers (fast), only decode geometry for candidates

Performance difference: 10-100x faster for spatial filters on large files.

Covering Metadata

GeoParquet 1.1+ includes "covering" metadata that tells query engines how to use bbox columns:

"covering": {
  "bbox": {
    "xmin": ["bbox", "xmin"],
    "ymin": ["bbox", "ymin"],
    "xmax": ["bbox", "xmax"],
    "ymax": ["bbox", "ymax"]
  }
}

This enables automatic optimization in tools like DuckDB and BigQuery.

How to Apply

# Add bbox column with metadata
gpio add bbox input.parquet output.parquet

# Add bbox metadata to existing bbox column
gpio add bbox-metadata myfile.parquet

# Convert with automatic bbox (default)
gpio convert input.shp output.parquet

Compression

Recommendations

Use Case Compression Level Rationale
General purpose ZSTD 15 Best balance of size and speed
Maximum compression ZSTD 22 Smaller files, slower write
Fast decompression LZ4 - Analytics workloads
Wide compatibility GZIP 6 Older tools

gpio uses ZSTD level 15 by default.

Why ZSTD?

  • 3-5x faster decompression than GZIP
  • Similar or better compression ratio
  • Widely supported in modern tools

How to Apply

# Default ZSTD compression
gpio convert input.shp output.parquet

# Maximum compression
gpio convert input.shp output.parquet --compression ZSTD --compression-level 22

# Fast decompression
gpio convert input.shp output.parquet --compression LZ4

Row Group Sizing

What Row Groups Are

Parquet files are divided into row groups - independent chunks that can be read separately. Each row group has its own statistics (min/max values).

Optimal Sizes

Metric Recommendation
Compressed size 50-100 MB per row group
Row count 50,000-150,000 rows (depends on data)

Why Size Matters

Too small: - Excessive metadata overhead - More seeks for sequential reads - Reduced compression efficiency

Too large: - Must read entire row group even for small queries - Higher memory usage during processing

How to Control

# Target row group size in MB
gpio extract input.parquet output.parquet --row-group-size-mb 64MB

# Exact row count
gpio extract input.parquet output.parquet --row-group-size 100000

Complete Optimization Pipeline

For a new file:

# 1. Convert with all optimizations (default)
gpio convert input.shp optimized.parquet

# 2. Verify optimizations
gpio check all optimized.parquet

For an existing GeoParquet file:

# 1. Check current state
gpio check all existing.parquet

# 2. Add bbox if missing
gpio add bbox existing.parquet with_bbox.parquet

# 3. Apply spatial ordering
gpio sort hilbert with_bbox.parquet optimized.parquet

# 4. Verify
gpio check all optimized.parquet

Or let gpio fix everything:

# Auto-fix all issues
gpio check all existing.parquet --fix --fix-output optimized.parquet

Measuring Improvement

Compare query performance before and after optimization:

# Time a spatial query
time duckdb -c "
  SELECT COUNT(*)
  FROM 'unoptimized.parquet'
  WHERE ST_Intersects(geometry, ST_GeomFromText('POLYGON(...)'))
"

time duckdb -c "
  SELECT COUNT(*)
  FROM 'optimized.parquet'
  WHERE ST_Intersects(geometry, ST_GeomFromText('POLYGON(...)'))
"

Typical improvements: 5-20x faster for spatial queries.

See Also