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NAD83 vs WGS84: Why Your Data Has a Slight Offset

Published: January 2025 Read time: 5 minutes

You've carefully aligned two datasets, but they're offset by about 1-2 meters. The roads don't quite match the parcels. The GPS points are slightly off from the imagery. What's going on?

The culprit is usually a datum mismatch between NAD83 and WGS84—two coordinate systems that look identical but aren't quite.

Quick Answer: NAD83 vs WGS84 Difference

In the continental US, NAD83 and WGS84 differ by approximately 1-2 meters. For most GIS work, this is negligible and you can treat them as equivalent. For survey-grade precision or legal boundaries, use proper datum transformations.

What Are NAD83 and WGS84?

Both are geodetic datums—mathematical models that define the Earth's shape and establish a coordinate origin.

Datum EPSG Code Primary Use
NAD83 4269 North American surveying, US government data
WGS84 4326 GPS, global applications, web maps

Key Difference

When NAD83 was established in 1986, it matched WGS84 almost exactly. But the North American plate moves about 2-3 cm per year. Over decades, this adds up.

How Big Is the Offset?

Location Approximate Offset
Continental US 1-2 meters
Alaska Up to 2 meters
Hawaii ~1 meter
Puerto Rico ~1 meter

The offset isn't constant—it varies by location and changes over time as the plate moves.

When Does This Matter?

Usually Doesn't Matter

Does Matter

Rule of thumb: If your project accuracy requirement is 5+ meters, treat NAD83 and WGS84 as equivalent. If you need sub-meter accuracy, use proper transformations.

How to Detect a Datum Mismatch

  1. Overlay two datasets that should align (e.g., roads on imagery)
  2. Check for systematic offset — Is everything shifted the same direction/distance?
  3. Measure the offset — 1-2 meters suggests NAD83/WGS84 mismatch
  4. Check the CRS definitions — Is one EPSG:4269 and the other EPSG:4326?

How to Fix It

Option 1: Accept the Offset (Usually Fine)

For most GIS work, 1-2 meters is within acceptable error. Don't over-engineer if you don't need survey precision.

Option 2: Transform Between Datums

If you need to eliminate the offset:

In QGIS

  1. Right-click layer → Export → Save Features As
  2. Set target CRS to the desired datum
  3. QGIS automatically applies the appropriate transformation

In Python (pyproj)

from pyproj import Transformer

# NAD83 to WGS84 with proper transformation
transformer = Transformer.from_crs(
    "EPSG:4269",  # NAD83
    "EPSG:4326",  # WGS84
    always_xy=True
)

# Transform a point
x_wgs84, y_wgs84 = transformer.transform(-122.4194, 37.7749)

In GDAL

ogr2ogr -s_srs EPSG:4269 -t_srs EPSG:4326 output.shp input.shp

Option 3: Redefine (Not Recommended)

You could simply redefine the CRS without transforming. This changes the label but not the coordinates. It works if you're treating them as equivalent, but it's technically incorrect for precision work.

NAD83 Versions

NAD83 has been updated several times:

Version Year Improvement
NAD83 (original) 1986 Initial realization
NAD83 (HARN) 1990s High Accuracy Reference Network
NAD83 (CORS96) 1996 CORS station adjustments
NAD83 (2011) 2011 Current US standard

Each version is slightly different. NAD83(2011) is current and most closely aligned with WGS84.

FAQ

What is the difference between NAD83 and WGS84?

Both are geodetic datums defining Earth's shape. In the continental US, they differ by 1-2 meters. NAD83 is fixed to North America; WGS84 is a global reference. For most GIS work, they're interchangeable.

Do I need to transform between NAD83 and WGS84?

For general GIS work (mapping, visualization, planning), no—treat them as equivalent. For survey-grade work, precision engineering, or legal boundaries, yes—use proper datum transformations.

Why does my data have a 1-2 meter offset?

A systematic 1-2 meter offset usually indicates a datum mismatch. One dataset is in NAD83, the other in WGS84, and they were overlaid without transformation. For most purposes, this is acceptable.

Is NAD83 the same as EPSG:4269?

Yes. EPSG:4269 is NAD83 geographic coordinates. EPSG:4326 is WGS84. Both use latitude/longitude in degrees but reference different datums, causing the 1-2 meter offset in North America.

Which should I use: NAD83 or WGS84?

Use NAD83 for US government data and surveying in North America. Use WGS84 for GPS data, web maps, and global applications. For general GIS work, either is fine.

Check Your Data's CRS

Upload your file to verify if it's NAD83, WGS84, or something else entirely.

Open Projection Finder

Summary

  1. NAD83 and WGS84 differ by 1-2 meters in North America
  2. For most GIS work, treat them as equivalent
  3. For survey precision, transform properly using pyproj, QGIS, or GDAL
  4. A systematic 1-2 meter offset usually means datum mismatch

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