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Difference between DSM and DEM

About 3DEP Products and Services

The 3DEP products and services available through The National Map consist of standard digital elevation models (DEMs) at various horizontal resolutions, elevation source and associated datasets, an elevation point query service and bulk point query service. All 3DEP products are available, free of charge and without use restrictions. To download 3DEP products visit: http://viewer.nationalmap.gov/basic/

For the latest information on 3DEP Products and Services, visit our 3DEP Product News page.


Standard DEMs represent the topographic surface of the earth and contain flattened water surfaces. Each DEM dataset is identified by its horizontal resolution and is produced to a consistent set of specifications. Standard DEMs are characterized either as project-based or seamless. Project-based DEMs are available for the full areal extents of projects when produced from light detection and ranging (lidar), or as one-degree blocks with overedge when produced from IfSAR. Seamless DEMs are produced by blending only the highest quality project data into a continuous terrain surface for the U.S. These data are distributed in tiles that can be merged to support analysis across large geographic areas.

Project-based

    • 1-meter – This dataset was introduced in 2015 with limited coverage of the U.S., but will be expanding as new DEMs from 3DEP quality level 2 or better lidar data are acquired. Horizontal coordinates are referenced to the Universal Transverse Mercator projection.
    • 1/9 arc-second – This dataset covers about 25 percent of the conterminous U.S. and is produced from 3-meter or higher resolution DEMs acquired by the USGS prior to January 2015. Horizontal coordinates are referenced to geographic coordinates (longitude, latitude). The 1/9 arc-second dataset will no longer be updated with newly acquired DEMs; however, it will continue to be distributed.
    • 5 meter – This dataset is comprised of 5-meter IfSAR-derived DEMs (3DEP quality level 5) over Alaska only. Horizontal coordinates are referenced to Albers Equal Area Conical projection.

Seamless*

    • 1/3 arc-second – This is the highest resolution seamless DEM dataset for the U.S. with full coverage of the 48 conterminous states, Hawaii, and U.S. territories. Alaska coverage is partially available now and is being expanded to statewide coverage as part of the Alaska Mapping Initiative. Ground spacing is approximately 10 meters north/south, but variable east/west due to convergence of meridians with latitude.
    • 1 arc-second – This is a lower resolution seamless dataset providing complete coverage over the conterminous U.S. and partial coverage of Alaska. Most of Canada and Mexico are also covered by the 1 arc-second dataset. Ground spacing is approximately 30 meters north/south, but variable east/west depending on latitude.
    • 2 arc-second – This seamless dataset is the lowest resolution seamless dataset available and covers only Alaska. Although ground spacing is approximately 60 meters north-south, east-west spacing can vary from 35 meters in southern Alaska to 20 meters on the North Shore.

Source Data Products include lidar point clouds, source (original) resolution DEMs from which the 3DEP standard DEM datasets were produced, and additional data types produced from IfSAR collections.
  • Lidar point cloud – These data are the foundational data for 3DEP in the conterminous U.S., and contain the original three-dimensional information from which the DEM products are derived. Most of the data collected in 2014 and later meet 3DEP specifications for quality level 2 nominal pulse spacing and vertical accuracy, and data collected prior to 2014 often do not meet the quality level 2 specification. Distinctions in nominal pulse spacing are provided in the lidar point cloud status graphics and in the download platform; however, other qualities such as vertical accuracy must be examined to determine if the data meet particular 3DEP quality level specifications.

  • IfSAR digital surface model (DSM) – These 5 meter rasters, available only in Alaska, are the initial IfSAR product, before bare-earth filtering is done to create the DEMs. Man-made structures and vegetation are modeled in the DSM.

  • IfSAR orthorectified radar intensity image (ORI) – These rasters (resolutions vary), available only in Alaska, are radar reflectance intensity recordings detected by the IfSAR sensor.

  • Source resolution DEMs – these data are the original bare earth DEMs derived from lidar point cloud source. Source DEM’s processed by the USGS after January 2015 are provided where the original DEM horizontal resolution or projection differ from the 3DEP standard DEM datasets.



Point Query Service

The National Map offers a point query service (PQS) that returns an elevation value for any latitude, longitude coordinate pair within the conterminous U.S. This service presently interpolates the elevation from the highest resolution seamless DEM dataset – 1/3 arc-second. This service is available at: http://nationalmap.gov/epqs.

A bulk point query service is available in a beta version at: http://viewer.nationalmap.gov/apps/. The Bulk Point Query allows users to upload a comma-separated (CSV) file containing: longitude and latitude points and returns the corresponding elevation values. Input is currently limited to no more than 500 points.

Elevation values from these services can be displayed on the screen and downloaded as a CSV or Excel formatted file that contains the original points and elevation values expressed in meters and feet.



* The seamless datasets are created from elevation data that are sourced from multiple technologies, positional accuracies and collection dates. Although these datasets are being continuously updated as new elevation source is acquired, much of the national coverage is derived from topographic map contours that may be decades old. The spatial metadata for each tile in a seamless DEM layer must be examined to fully determine the source datasets used to create each tile.


 


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Page Last Modified: Friday, 16-Dec-2016 10:25:17 EST