Understanding Geographic Coordinate Systems: A Practical Guide
Learn the fundamentals of geographic coordinate systems, from WGS84 to UTM zones, and when to use each one for your mapping projects.
Table of Contents
Geographic coordinate systems are the foundation of all mapping and geospatial work. Whether you’re building a mobile app with location features or analyzing satellite imagery, understanding how coordinates work is essential.
What is a Coordinate Reference System (CRS)?
A Coordinate Reference System defines how geographic locations are represented as numbers. It consists of:
- Datum: The mathematical model of Earth’s shape
- Projection: How the 3D Earth is flattened onto a 2D surface
- Units: Degrees, meters, feet, etc.
Common Coordinate Systems
WGS84 (EPSG:4326)
The World Geodetic System 1984 is the most widely used global reference system. It’s what GPS uses and what most web maps expect.
- Format: Latitude/Longitude in decimal degrees
- Range: Latitude -90° to 90°, Longitude -180° to 180°
- Best for: Global data, GPS coordinates, web mapping
Example: San Francisco is at 37.7749, -122.4194
Web Mercator (EPSG:3857)
Web Mercator is a projected coordinate system used by Google Maps, OpenStreetMap, and most web mapping libraries.
- Format: X/Y in meters
- Pros: Preserves shapes, easy tile math
- Cons: Severe area distortion at high latitudes
UTM Zones
Universal Transverse Mercator divides the world into 60 zones, each 6° wide. It’s excellent for local work because it minimizes distortion within each zone.
- Format: Easting/Northing in meters
- Best for: Local surveys, construction, military applications
- Zone selection: Use the zone containing your area of interest
When to Use Each System
| Use Case | Recommended CRS |
|---|---|
| Storing GPS data | WGS84 (EPSG:4326) |
| Web map display | Web Mercator (EPSG:3857) |
| Area calculations | UTM or local projection |
| Distance measurements | UTM or local projection |
| Global analysis | WGS84 with appropriate projection |
Converting Between Systems
Coordinate conversion requires knowing both the source and destination CRS. Our Coordinate Converter tool supports over 120 coordinate systems, including all UTM zones.
Key considerations when converting:
- Precision loss: Some conversions involve approximations
- Datum shifts: Different datums can shift points by meters
- Zone boundaries: UTM conversions require the correct zone
Practical Tips
- Always document your CRS: Include the EPSG code in your data
- Validate coordinates: Check that values are within valid ranges
- Use the right precision: GPS accuracy is ~3-5 meters, so 6 decimal places is usually sufficient
- Consider your use case: Choose projections that minimize distortion for your specific application
Learn More
- EPSG.io - Comprehensive CRS database
- Proj4js - JavaScript coordinate transformation library
- Our GeoJSON Viewer for visualizing geographic data