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National Elevation Dataset
The National Elevation Dataset (NED) consists of high precision topography or ground surface elevation data (digital elevation model) for the United States. It was maintained by the USGS and all the data is in the public domain. Since the 3D Elevation Program came online, the NED was subsumedThe National Map elevation informati/ref> into The National Map as one of its layers of information. Sources The NED dataset is a compilation of data from a variety of existing high-precision datasets such as LiDAR data (see also National LIDAR Dataset - USA), contour maps, USGS DEM collection, SRTM and other sources which were reorganized and combined into a seamless dataset, designed to cover all the United States territory in its continuity. Formats Data is available in a few popular formats such as ESRI ArcGRID, GeoTIFF, BIL, GridFloat, and a few others. Precision Depending on area location, the datasets are provided with 1/9 (about 3 meters), 1/3 (about 10 m) and 1-arcsecond A m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief, but also natural, artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically ''relief'', even though the USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on. Topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms; this is also known as geomorphometry. In modern usage, this involves generation of elevation data in digital form (DEM). It is often considered to include the graphic representation of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contour Line
A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensional graph of the function f(x,y) parallel to the (x,y)-plane. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines. The gradient of the function is always perpendicular to the contour lines. When the lines are close together the magnitude of the grad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth circumference is very near . A minute of arc is of a radian. A second of arc, arcsecond (arcsec), or arc second, denoted by the symbol , is of an arcminute, of a degree, of a turn, and (about ) of a radian. These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship. To express even smaller angles, standard SI prefixes can be employed; the milliarcsecond (mas) and microarcsecond (μas), for instance, are commonly used in astron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ArcView
ArcView is the entry level licensing level of ArcGIS Desktop, a geographic information system software product produced by Esri. It is intended by Esri to be the logical migration path from ArcView 3.x. ArcView is now referred to as ArcGIS for Desktop Basic. See also ST-Links PgMap* ArcInfo * Shapefile * ArcView 3.x History ArcView 8.x and 9.x ArcView 8.x and 9.x are part of the ArcGIS Desktop software suite. ArcView is the entry level of licensing offered, it is able to view & edit GIS data held in a flat file database or, through ArcSDE, ST-Links PgMapview data held in a relational database management system. Other licensing levels in the suite, namely ArcEditor and ArcInfo have greater functionality. All components are installed on the system, with only those that are licensed being made functional. The current version of ArcView sold by Esri is 10. The ArcView software is split between ArcMap & ArcCatalog. ArcMap is used for map composition and geographic analysis. ArcC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GeoTIFF
GeoTIFF is a public domain metadata standard which allows georeferencing information to be embedded within a TIFF file. The potential additional information includes map projection, coordinate systems, ellipsoids, datums, and everything else necessary to establish the exact spatial reference for the file. The GeoTIFF format is fully compliant with TIFF 6.0, so software incapable of reading and interpreting the specialized metadata will still be able to open a GeoTIFF format file. An alternative to the "inlined" TIFF geospatial metadata is the *.tfw World File sidecar file format which may sit in the same folder as the regular TIFF file to provide a subset of the functionality of the standard GeoTIFF described here. History The GeoTIFF format was originally created by Dr. Niles Ritter while he was working at the NASA Jet Propulsion Laboratory. The reference implementation code was released mostly as public domain software with some parts under a permissive X license. On Septembe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Environmental Systems Research Institute
Esri (; Environmental Systems Research Institute) is an American multinational geographic information system (GIS) software company. It is best known for its ArcGIS products. With a 43% market share, Esri is the world's leading supplier of GIS software, web GIS and geodatabase management applications. The company is headquartered in Redlands, California. Founded as the Environmental Systems Research Institute in 1969 as a land-use consulting firm, Esri currently has 49 offices worldwide including 11 research and development centers in the United States, Europe, the Middle East and Africa and Asia Pacific. There are 10 regional U.S. offices and over 3,000 partners globally, with users in every country and a total of over a million active users in 350,000 organizations. These include Fortune 500 companies, most national governments, 20,000 cities, all 50 US States and 7,000+ universities. The firm has 4,000 total employees, and is privately held by its founders. In a 2016 Investo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SRTM
The Shuttle Radar Topography Mission (SRTM) is an international research effort that obtained digital elevation models on a near-global scale from 56°S to 60°N, to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER GDEM in 2009. SRTM consisted of a specially modified radar system that flew on board the Space Shuttle Endeavour during the 11-day STS-99 mission in February 2000. The radar system was based on the older '' Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar'' (SIR-C/X-SAR), previously used on the Shuttle in 1994. To acquire topographic data, the SRTM payload was outfitted with two radar antennas. One antenna was located in the Shuttle's payload bay, the other – a critical change from the SIR-C/X-SAR, allowing single-pass interferometry – on the end of a 60-meter (200-foot) mast that extended from the payload bay once the Shuttle was in space. The technique employed is known as interferomet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
USGS DEM
The USGS DEM standard is a geospatial file format developed by the United States Geological Survey for storing a raster-based digital elevation model. It is an open standard, and is used throughout the world. It has been superseded by the USGS's own SDTS format but the format remains popular due to large numbers of legacy files, self-containment, relatively simple field structure and broad, mature software support. DEM Level A USGS DEM can be classified into one of four levels of quality. This is due to the multiple methods of data collection, and certainty in the data. Format Structure The USGS DEM format is a self-contained (single file) set of ASCII-encoded (text) 1024-byte (1024 ASCII chars) blocks that fall into three record categories called A, B, and C. There is no cross-platform ambiguity since line ending control codes are not used, and all data including numbers is represented in readable text form. There is no known binary analogue of the format, although it is common pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
National LIDAR Dataset - USA
Currently, the best source for nationwide LiDAR availability from public sources is the United States Interagency Elevation Inventory (USIEI). The USIEI is a collaborative effort of NOAA and the U.S. Geological Survey, with contributions from the Federal Emergency Management Agency, the Natural Resources Conservation Service, the US Army Corps of Engineers, and the National Park Service. The inventory displays high-accuracy topographic and bathymetric data for the US, and it's intended to be a comprehensive, nationwide listing of known high-accuracy topographic data, including lidar. The inventory is updated semi-annually. Note, however, that getting access to the data is often less than straightforward in the current implementation. History: In the United States, the United States Geological Survey (USGS) was the lead agency coordinating efforts across multiple agencies towards a National LIDAR Dataset. The first meeting, a National LIDAR Initiative Strategy Meeting, was held at USG ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Elevation Model
A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps. A digital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs. While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies, geological applications, and other applications, and in planetary science. Terminology There is no universal usage of the terms ''digital elevation model'' (DEM), ''digital terrain model'' (DTM) and ''digital surface model'' (DSM) in scientific literature. In most cases the term ''digital ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LiDAR
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be used to make digital 3-D representations of areas on the Earth's surface and ocean bottom of the intertidal and near coastal zone by varying the wavelength of light. It has terrestrial, airborne, and mobile applications. ''Lidar'' is an acronym of "light detection and ranging" or "laser imaging, detection, and ranging". It is sometimes called 3-D laser scanning, a special combination of 3-D scanning and laser scanning. Lidar is commonly used to make high-resolution maps, with applications in surveying, geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. It is also used in control and navigation for som ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The National Map
''The National Map'' is a collaborative effort of the United States Geological Survey (USGS) and other federal, state, and local agencies to improve and deliver topographic information for the United States. The purpose of the effort is to provide "...a seamless, continuously maintained set of public domain geographic base information that will serve as a foundation for integrating, sharing, and using other data easily and consistently". ''The National Map'' is part of the USGS National Geospatial Program. The geographic information available includes orthoimagery (aerial photographs), elevation, geographic names, hydrography, boundaries, transportation, structures and land cover. ''The National Map'' is accessible via the Web, as products and services, and as downloadable data. Its uses range from recreation to scientific analysis to emergency response. ''The National Map'' is a significant contribution to the U.S. National Spatial Data Infrastructure (NSDI) from the Federa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
