Are 3D Elevation Program (3DEP) contour lines updated and what sources were used to create them?

Yes, depression contours are identified with tick marks in 3D Elevation Program products, but only in large scale contours (1:36,000 scale to 1:18,000 scale).

Contours are not projected, but are provided in geographic coordinates (latitude and longitude) in units of decimal degrees, and horizontally referenced to the North American Datum of 1983. Contour elevation values are vertically referenced to the North American Vertical Datum of 1988. Contours are staged in Esri File Geodatabase 10.1 or Shapefile format, and distributed in 1x1 degree tiles.

3D Elevation Program (3DEP) contours cover all of the United States and its territories at multiple scales: Small scales (1:578,000-1:289,000) Medium scales (1:144,000-1:72,000) Large scales (1:36,000-1:18,000) Contours are easily viewed in The National Map Viewer and USGS topographic maps , or downloaded through The National Map Download Client . Learn more: Map Scales

If you think you’ve found an error in USGS elevation data, please send an email to tnm_help@usgs.gov. We will add the reported information to our "Digital Elevation Model Issues" data log for further analysis and possible correction. Spikes, pits, seam-line anomalies, and other data errors are of concern to us. We are working to correct or minimize known issues, but it will take some time. Errors...

Elevations provided by your GPS receiver might disagree with elevations on a USGS map, but they could both be correct if they reference different vertical and/or horizontal datums. The default horizontal datum setting on most GPS receivers is the World Geodetic System of 1984 (WGS84) and the elevations are based on the NAD83 ellipsoid. USGS topographic maps published after 2009 are georeferenced...

The National Map’s   Elevation Point Query Service (EPQS) returns elevations that are interpolated from the 3DEP dynamic elevation service. This is a web coverage service (WCS) that includes multiple resolutions of DEMs including 1 meter resolution lidar-based DEMs where available, and 1/3 arc-second seamless DEMs. The accuracy of the elevations returned by EPQS will vary according to the source...

The U.S. Geological Survey (USGS) has been the primary civilian mapping agency of the United States since 1879. Some of the most well-known USGS maps are the 1:24,000-scale topographic maps, also called 7.5-minute  quadrangles . In 2009, the USGS transitioned from our hand scribed historical topographic maps to US Topos , which are computer-generated on a regular schedule using national databases...

Digital elevation data for the United States and its territories are available through The National Map Downloader . Click the “Help” link at the top of the page for detailed instructions on how to find and download data. There's a separate site for The National Map Services . Downloads and map services are free; no account is required. The 3D Elevation Program (3DEP) products and services...