What does "georeferenced" mean?

Georeferencing means that the internal coordinate system of a map or aerial photo image can be related to a ground system of geographic coordinates. The relevant coordinate transforms are typically stored within the image file (GeoPDF and GeoTIFF are examples), though there are many possible mechanisms for implementing georeferencing. The most visible effect of georeferencing is that display software can show ground coordinates (such as latitude/longitude or UTM coordinates) and also measure ground distances and areas. Doing these things with USGS GeoPDF maps requires the free TerraGo toolbar extension to Adobe Reader.

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What is a geographic information system (GIS)?

A Geographic Information System (GIS) is a computer system that analyzes and displays geographically referenced information. It uses data that is attached to a unique location. Most of the information we have about our world contains a location reference: Where are USGS streamgages located? Where was a rock sample collected? Exactly where are all...

What does the term UTM mean? Is UTM better or more accurate than latitude/longitude?

UTM is the acronym for Universal Transverse Mercator, a plane coordinate grid system named for the map projection on which it is based (Transverse Mercator). The UTM system consists of 60 zones, each 6-degrees of longitude in width. The zones are numbered 1-60, beginning at 180-degrees longitude and increasing to the east. The military uses their...

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...

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 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.

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October 27, 2015

Using US Topo and Historic Topo Maps on your Mobile Device

Lesson 6a: Using USGS US Topo and Historic Topographic Maps on your Mobile Device - This video demonstrates how to download and use US Topo and Historic Topographic maps on a mobile device.

video thumbnail: Elevation
April 30, 2012

Elevation

The National Elevation Dataset (NED) is the primary elevation data product produced and distributed by the USGS National 3D Elevation Program (3DEP). The NED provides seamless raster elevation data of the conterminous United States, Alaska, Hawaii, and the island territories. The NED is derived from diverse source data sets that are processed to a specification with a

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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
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Image: USGS Topographers at Work
March 14, 1984

USGS Topographers at Work

USGS topographers making an electronic distance measurement in a dry lake bed in Saline Valley in Death Valley, California.