geohash-coloring

Geohash Coloring Skill

GF(3) colored geohashes for hierarchical spatial indexing with deterministic color derivation.

Trigger

• Geohash encoding/decoding
• Hierarchical spatial clustering
• Location-based coloring schemes
• Privacy-preserving location representation

GF(3) Trit: +1 (Generator)

Generates colored spatial identifiers from coordinates.

Geohash Basics

Geohash encodes lat/lon into a string where:

• Longer = more precise
• Prefix = parent cell
• Adjacent cells share prefixes

Precision | Cell Width | Cell Height
    1     |  5,009 km  |  4,992 km
    2     |  1,252 km  |    624 km
    3     |    156 km  |    156 km
    4     |     39 km  |     19 km
    5     |      5 km  |      5 km
    6     |    1.2 km  |    0.6 km
    7     |    153 m   |    153 m
    8     |     38 m   |     19 m
    9     |      5 m   |      5 m

Core Implementation

import hashlib

# Geohash alphabet (base32)
GEOHASH_CHARS = '0123456789bcdefghjkmnpqrstuvwxyz'

def encode_geohash(lat: float, lon: float, precision: int = 9) -> str:
    """Encode lat/lon to geohash string."""
    lat_range = (-90.0, 90.0)
    lon_range = (-180.0, 180.0)
    
    geohash = []
    bits = 0
    bit_count = 0
    is_lon = True
    
    while len(geohash) < precision:
        if is_lon:
            mid = (lon_range[0] + lon_range[1]) / 2
            if lon >= mid:
                bits = (bits << 1) | 1
                lon_range = (mid, lon_range[1])
            else:
                bits = bits << 1
                lon_range = (lon_range[0], mid)
        else:
            mid = (lat_range[0] + lat_range[1]) / 2
            if lat >= mid:
                bits = (bits << 1) | 1
                lat_range = (mid, lat_range[1])
            else:
                bits = bits << 1
                lat_range = (lat_range[0], mid)
        
        is_lon = not is_lon
        bit_count += 1
        
        if bit_count == 5:
            geohash.append(GEOHASH_CHARS[bits])
            bits = 0
            bit_count = 0
    
    return ''.join(geohash)

def decode_geohash(geohash: str) -> tuple[float, float, float, float]:
    """Decode geohash to bounding box (lat_min, lat_max, lon_min, lon_max)."""
    lat_range = [-90.0, 90.0]
    lon_range = [-180.0, 180.0]
    is_lon = True
    
    for char in geohash:
        idx = GEOHASH_CHARS.index(char.lower())
        for i in range(4, -1, -1):
            bit = (idx >> i) & 1
            if is_lon:
                mid = (lon_range[0] + lon_range[1]) / 2
                if bit:
                    lon_range[0] = mid
                else:
                    lon_range[1] = mid
            else:
                mid = (lat_range[0] + lat_range[1]) / 2
                if bit:
                    lat_range[0] = mid
                else:
                    lat_range[1] = mid
            is_lon = not is_lon
    
    return lat_range[0], lat_range[1], lon_range[0], lon_range[1]

def geohash_center(geohash: str) -> tuple[float, float]:
    """Get center point of geohash cell."""
    lat_min, lat_max, lon_min, lon_max = decode_geohash(geohash)
    return (lat_min + lat_max) / 2, (lon_min + lon_max) / 2