How large is the North American Datum (NAD) 27 to NAD 83 shift?

Within the conterminous 48 states, the NAD27-NAD83 shift of the latitude/longitude graticule (lines showing parallels of latitude and meridians of longitude for the earth) is in the range of 10-100 ground meters. Changes to UTM values are generally larger, around 200 meters, and changes for other coordinate systems are different. For more detail about the effects of datum changes on USGS quadrangle maps, see this technical paper.

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Why are the historical maps referenced to outdated datums?

Many different datums exist, but in the United States only three datums are commonly used: The North American Datum of 1927 ( NAD27 ) uses a starting point at a base station in Meades Ranch, Kansas and the Clarke Ellipsoid to calculate the shape of the Earth. The North American Datum of 1983 ( NAD83 ) was developed when satellites enabled a better...

Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong?

The old coordinates were not wrong, just different. They are based on different earth shapes or ellipsoids and were based on the best technology at the time. Mathematically, NAD83 is a stronger datum because all previously existing horizontal stations and newer GPS surveyed stations were adjusted simultaneously. The positions within NAD27 were...

How are different map projections used?

The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way. A flat map can show one or more--but never all--...

What location coordinates (datum) does the Geographic Names Information System use?

All coordinates in the Geographic Names Information System database are in the North American Datum of 1983 (NAD 83). They were converted from the North American Datum of 1927 (NAD 27) in September 2005.
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Date published: October 23, 2019

USGS Digital Elevation Models (DEM) Switching to New Distribution Format

In support of ongoing efforts to provide efficient, cloud ready, open data formats, the U.S. Geological Survey National Geospatial Program is announcing plans to migrate its 3D Elevation Program (3DEP) Digital Elevation Models (DEM) to a new data delivery format called Cloud Optimized Geotiff (COG) during the first half of fiscal year 2020.

Date published: July 31, 2017

Mapping Public Lands in the United States

The Protected Areas Database of the United States (PAD-US) is the official inventory of public parks and other protected areas in all U.S. states and territories.

Date published: July 7, 2015

A New Way to Find Old Maps

How did your neighborhood look in the 1900s?  Now there’s an easier way to find out.

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November 18, 2004

PubTalk 11/2004 — From Plane Tables to Pixels

The Revolution in Mapping at the U.S. Geological Survey

by Susan P. Benjamin, Research Geographer

  • Mapping the United States in the 19th century was arduous, dangerous work; flash floods, bears, and bandits were just a few hazards
  • By the mid-20th century, aerial photography, photogrammetry, and stereophoto pairs, allowed
Image: USGS Topographers at Work
January 1, 1926

USGS Topographers at Work

Two topographers working with an alidade and plane table. The man on the right is believed to be Roland Whitman Burchard, who was the topographer for the USGS Grand Canyon Expedition of 1923. Author Lewis Freeman described Burchard as a man of "powerful physique, great endurance, and a cool, steady hand."

This is a USGS Ed Resource thumbnail.
April 25, 2019

Datum Shifts

Attribution: Science Support