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Georeferencing means that the internal coordinate system of a digital map or aerial photo can be related to a ground system of geographic coordinates. A georeferenced digital map or image has been tied to a known Earth coordinate system, so users can determine where every point on the map or aerial photo is located on the Earth's surface.
The relevant coordinate transforms are typically stored within the image file (GeoPDF and GeoTIFF are examples of georeferenced file formats), though there are many possible mechanisms for implementing georeferencing. Georeferencing in the digital file allows basic map analysis to be done, such as pointing and clicking on the map to determine the coordinates of a point, to calculate distances and areas, and to determine other information.
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--of the following: True directions True distances...
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, and changes for other coordinate systems are...
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 of a city's fire hydrants? If, for example, a rare...
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 own implementation of the UTM system, called the...
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.
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.
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 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 Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
USGS topographers making an electronic distance measurement in a dry lake bed in Saline Valley in Death Valley, California.
USGS topographers making an electronic distance measurement in a dry lake bed in Saline Valley in Death Valley, California.
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--of the following: True directions True distances...
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, and changes for other coordinate systems are...
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 of a city's fire hydrants? If, for example, a rare...
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 own implementation of the UTM system, called the...
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.
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.
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 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 Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
USGS topographers making an electronic distance measurement in a dry lake bed in Saline Valley in Death Valley, California.
USGS topographers making an electronic distance measurement in a dry lake bed in Saline Valley in Death Valley, California.