Maps and Mapping
How do I find, download, or order topographic maps?
What types of elevation datasets are available, what formats do they come in, and where can I download them?
What is a Digital Orthophoto Quadrangle (DOQ) or an orthoimage?
The USGS provides the mapping and digital geospatial foundation for the Nation.
Will I be able to see my house in an aerial photograph? Will enlarging the image let me see more detail?
The ability to see specific items in an aerial image is mostly a function of scale and resolution. The following aerial photography products all have a resolution of 1 meter or better, so you should be able to see an object the size of a house: High Resolution Orthoimagery (HRO) National Agriculture Imagery Program (NAIP) imagery Digital Orthophoto Quadrangle (DOQ) Use EarthExplorer to search for...
Are depression contours identified in 3D Elevation Program (3DEP) contour products?
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).
At what scales are contours visible in The National Map Viewer?
In the default base map for The National Map Advanced Viewer : 500-foot contours are visible at a scale of 1:578,000 (zoom level 10) 100-foot contours are visible at scales of 1:289,000-1:144,000 (zoom level 11-12) 50-foot contours are visible at a scale of 1:72,000 (zoom level 13) Large scale contours are visible at scales from 1:36,000-1:9,000 (zoom levels 14-16)
What geographic areas do 3D Elevation Program (3DEP) contours cover?
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
Are 3D Elevation Program (3DEP) contour lines updated and what sources were used to create them?
When significant changes in the landscape have occurred, contours will be updated on an as-needed basis. The 100-foot contours were derived from 3DEP (formerly National Elevation Dataset) one arc-second resolution data that was sub-sampled to a cell size of three arc-second. The 50-foot contours were also derived from one arc-second data. Large-scale contours were derived from 1/3 arc-second...
What are the projection, horizontal and vertical datum, format, and distributed tile extent of 3D Elevation Program (3DEP) contours?
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.
Why are two different file naming conventions used in distribution of 3D Elevation Program (3DEP) DEM products?
Updated digital elevation model (DEM) dataset files are now given a name that includes information about the resolution and format of the data. This prevents users from accidentally overwriting existing data that might have different resolutions and formats. For example: an older file: n44w071.zip would now have the name: USGS_13_n44w071.tif indicating 1/3 arc-second elevation data in geotiff...
What data sources are used to produce the 3D Elevation Program (3DEP) DEMs?
The USGS 3D Elevation Program (3DEP) is in the process of collecting high-quality lidar and IfSAR (for Alaska) coverage for all of the United States and its territories. As this new data becomes available, legacy Digital Elevation Models (DEMs) are being systematically replaced with high-resolution DEMs produced almost entirely from the lidar and ifsar data. Legacy DEMs were produced from...
What map projections are used in The National Map tiled base map services and dynamic overlay services?
The projection used for all tiled base map services in The National Map is the World Geodetic System 1984 (WGS 84) Web Mercator (Auxiliary Sphere) so that base map services can be used in combination with other common viewers. See Spatial Reference SR-ORG:6928 and Spatial Reference SR-ORG:7483 . Dynamic overlay services are in WGS84 (see Spatial Reference EPSG:4326 ) but can be reprojected as...
How often are The National Map's composite base maps and dynamic service overlays updated?
Composite base maps are recached about once a year. Although data in dynamic service overlays are ideally updated quarterly, it can sometimes take up to six months. Please note that there will be times when composite base maps and dynamic service overlays are not in synchronization because of a difference in refresh cycles. Subscribe to the National Map Simple Notifcation Service (SNS) to stay in...
What is the difference between tiled and dynamic services?
A tiled service contains cached tiles that render the map in small tile images. This allows the map to perform much faster when panning and zooming, compared to a dynamic service. Dynamic is considered an "older" way of displaying web maps, where each feature is called from the source data and drawn separately for every pan and zoom. Tiled base maps are cached from global scale to a scale of 1:9...
What are the base map services (or URLs) used in The National Map?
The National Map Services offers a series of composite base maps that combine layers into tile cache services with the cartographic richness of multiple data sources. The following base maps are available: USGS Topo - combines the most current data (boundaries, geographic names, transportation, elevation, hydrography, land cover, and other themes) that make up The National Map. Contours generated...