Why don't the elevations on your maps agree with those provided by my GPS system? Which ones are correct?

They both might be correct. The reason that the elevations do not agree might be because they are set on different datums. Most maps use NAD27 and the elevations are based on mean sea level. Your GPS receiver uses WGS84 and the elevations are based on the NAD83 ellipsoid. These datum shifts can result in difference of tens of meters horizontal and hundreds of meters vertically.

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What is Lidar data and where can I download it?

Light Detection and Ranging ( lidar ) is a technology used to create high-resolution models of ground elevation with a vertical accuracy of 10 centimeters (4 inches). Lidar equipment, which includes a laser scanner, a Global Positioning System (GPS), and an Inertial Navigation System (INS), is typically mounted on a small aircraft. The laser...

What is the projection, horizontal datum, vertical datum, and resolution for a USGS digital elevation model DEM?

Projection :  3DEP DEMS have different projections/coordinate systems depending on the product: 1/3-, 1-, and 2-arc-second (also the discontinued 1/9-arc-second) DEMs are not projected. They are all in geographic coordinates (latitude/longitude). 5-meter DEMs (Alaska only) are Alaska Albers Equal Area. 1-meter DEMs are in Universal Transverse...

What is a digital elevation model (DEM)?

A Digital Elevation Model (DEM) is a representation of the bare ground (bare earth) topographic surface of the Earth excluding trees, buildings, and any other surface objects.  DEMs are created from a variety of sources. USGS DEMs used to be derived primarily from topographic maps . Those are being systematically replaced with DEMs derived from...

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

Within the conterminous 48 states, the North American Datum of 1927 (NAD 27) to the North American Datum of 1983 (NAD 83) 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,...

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--...
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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: February 7, 2019

USGS 3DEP Lidar Point Cloud Now Available as Amazon Public Dataset

The USGS 3D Elevation Program (3DEP) is excited to announce the availability of a new way to access and process lidar point cloud data from the 3DEP repository.

Date published: July 19, 2017

Historical Maps at Your Fingertips

Earlier this month, the USGS launched “TopoView 2.1”, an enhancement to the current popular TopoView mapping service that lets users discover, interact, and download historical USGS topographic maps scans.

Date published: April 19, 2012

Historical Maps Go Digital

In 1884, the second USGS Director John Wesley Powell briefed Congress on the need for a national mapping program, stating, "The map once constructed should be enduring…"   

Date published: December 8, 2009

A new generation of topographic maps

A new generation of topographic maps will be discussed at a free public lecture in Menlo Park this Thursday, December 10, 2009. The maps, available free from the U.S. Geological Survey online store, are customizable, provide richer content, and can be printed for immediate use.

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Ben Jones looking at a GPS station
April 19, 2017

Ben Jones with a GPS station

Ben Jones with a GPS station

man walking along wet sand on beach wearing a backpack with an antenna sticking pout of it
January 31, 2017

Mapping the beach with a GPS-equipped backpack unit.

USGS scientist Daniel Hoover mapping the beach at Santa Cruz with a GPS-equipped backpack unit.

small excerpt of Yosemite Valley topographic map in shades of green and brown
August 31, 2016

Topographic map excerpt of Yosemite Valley

Exerpt from USGS Half Dome quadrangle topographic map showing Yosemite Valley.

Image: GPS Tracks Ground Deformation
August 16, 2011

GPS Tracks Ground Deformation

USGS Field Engineer Ben Pauk records site and equipment information for the Global Positioning System (GPS) installed at the North Rim station in the Newberry National Volcanic Monument. The GPS records the precise position of the station, including latitude, longitude and elevation. Tracking subtle ground deformation through GPS provides insight into how volcanoes can

Image: Learning How to Navigate With GPS
June 25, 2011

Learning How to Navigate With GPS

USGS SIS employees led a GPS class in the Kid Zone at the Longmont Airshow.

Attribution: Water Resources
Image: Learning How to Navigate With GPS
June 25, 2011

Learning How to Navigate With GPS

USGS SIS employees led a GPS class in the Kid Zone at the Longmont Airshow.

Attribution: Water Resources
Image: USGS Elevation Monument
January 1, 1905

USGS Elevation Monument

USGS elevation monument for a level line run from Mojave, California to Keeler, California. The line ran through such places as 18-Mile Station, Dixie, Indan Wells, Little Lake, and Olancha. Elevations were based on Benecia datum.

National Elevation Dataset

National Elevation Dataset

National Elevation Dataset