In modern mapping, a topographic map or topographic sheet is a type of map characterized by large-scale detail and quantitative representation of relief features, usually using contour lines (connecting points of equal elevation), but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and artificial features.A topographic survey is typically based upon systematic observation and published as a map series, made up of two or more map sheets that combine to form the whole map. A topographic map series uses a common specification that includes the range of cartographic symbols employed, as well as a standard geodetic framework that defines the map projection, coordinate system, ellipsoid and geodetic datum. Official topographic maps also adopt a national grid referencing system.
Natural Resources Canada provides this description of topographic maps:
These maps depict in detail ground relief (landforms and terrain), drainage (lakes and rivers), forest cover, administrative areas, populated areas, transportation routes and facilities (including roads and railways), and other man-made features.
Other authors define topographic maps by contrasting them with another type of map; they are distinguished from smaller-scale "chorographic maps" that cover large regions,"planimetric maps" that do not show elevations, and "thematic maps" that focus on specific topics.
However, in the vernacular and day to day world, the representation of relief (contours) is popularly held to define the genre, such that even small-scale maps showing relief are commonly (and erroneously, in the technical sense) called "topographic".
The study or discipline of topography is a much broader field of study, which takes into account all natural and man-made features of terrain. Maps were among the first artifacts to record observations about topography.
Topographic maps are based on topographical surveys. Performed at large scales, these surveys are called topographical in the old sense of topography, showing a variety of elevations and landforms.This is in contrast to older cadastral surveys, which primarily show property and governmental boundaries. The first multi-sheet topographic map series of an entire country, the Carte géométrique de la France, was completed in 1789. The Great Trigonometric Survey of India, started by the East India Company in 1802, then taken over by the British Raj after 1857 was notable as a successful effort on a larger scale and for accurately determining heights of Himalayan peaks from viewpoints over one hundred miles distant.
Topographic surveys were prepared by the military to assist in planning for battle and for defensive emplacements (thus the name and history of the United Kingdom's Ordnance Survey). As such, elevation information was of vital importance.
As they evolved, topographic map series became a national resource in modern nations in planning infrastructure and resource exploitation. In the United States, the national map-making function which had been shared by both the Army Corps of Engineers and the Department of the Interior migrated to the newly created United States Geological Survey in 1879, where it has remained since.
1913 saw the beginning of the International Map of the World initiative, which set out to map all of Earth's significant land areas at a scale of 1:1 million, on about one thousand sheets, each covering four degrees latitude by six or more degrees longitude. Excluding borders, each sheet was 44 cm high and (depending on latitude) up to 66 cm wide. Although the project eventually foundered, it left an indexing system that remains in use.
By the 1980s, centralized printing of standardized topographic maps began to be superseded by databases of coordinates that could be used on computers by moderately skilled end users to view or print maps with arbitrary contents, coverage and scale. For example, the federal government of the United States' TIGER initiative compiled interlinked databases of federal, state and local political borders and census enumeration areas, and of roadways, railroads, and water features with support for locating street addresses within street segments. TIGER was developed in the 1980s and used in the 1990 and subsequent decennial censuses. Digital elevation models (DEM) were also compiled, initially from topographic maps and stereographic interpretation of aerial photographs and then from satellite photography and radar data. Since all these were government projects funded with taxes and not classified for national security reasons, the datasets were in the public domain and freely usable without fees or licensing.
TIGER and DEM datasets greatly facilitated geographic information systems and made the Global Positioning System much more useful by providing context around locations given by the technology as coordinates. Initial applications were mostly professionalized forms such as innovative surveying instruments and agency-level GIS systems tended by experts. By the mid-1990s, increasingly user-friendly resources such as online mapping in two and three dimensions, integration of GPS with mobile phones and automotive navigation systems appeared. As of 2011, the future of standardized, centrally printed topographical maps is left somewhat in doubt.
Topographic maps have many multiple uses in the present day: any type of geographic planning or large-scale architecture; earth sciences and many other geographic disciplines; mining and other earth-based endeavours; civil engineering and recreational uses such as hiking and orienteering.
The various features shown on the map are represented by conventional signs or symbols. For example, colors can be used to indicate a classification of roads. These signs are usually explained in the margin of the map, or on a separately published characteristic sheet.
Topographic maps are also commonly called contour maps or topo maps. In the United States, where the primary national series is organized by a strict 7.5-minute grid, they are often called or quads or quadrangles.
Topographic maps conventionally show topography, or land contours, by means of contour lines. Contour lines are curves that connect contiguous points of the same altitude (isohypse). In other words, every point on the marked line of 100 m elevation is 100 m above mean sea level.
These maps usually show not only the contours, but also any significant streams or other bodies of water, forest cover, built-up areas or individual buildings (depending on scale), and other features and points of interest such as what direction those streams are flowing.
Most topographic maps were prepared using photogrammetric interpretation of aerial photography using a stereoplotter. Modern mapping also employs lidar and other Remote sensing techniques. Older topographic maps were prepared using traditional surveying instruments.
The cartographic style (content and appearance) of topographic maps is highly variable between national mapping organizations. Aesthetic traditions and conventions persist in topographic map symbology, particularly amongst European countries at medium map scales.
Although virtually the entire terrestrial surface of Earth has been mapped at scale 1:1,000,000, medium and large-scale mapping has been accomplished intensively in some countries and much less in others.Nevertheless, national mapping programs listed below are only a partial selection. Several commercial vendors supply international topographic map series.
Cartography is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.
A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.
A digital elevation model (DEM) is a 3D computer graphics representation of elevation data to represent terrain, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems, and are the most common basis for digitally produced relief maps.
Topography is the study of the forms and features of land surfaces. The topography of an area could refer to the surface forms and features themselves, or a description.
Terrain or relief involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word terra means "earth."
An orthophoto, orthophotograph or orthoimage is an aerial photograph or satellite imagery geometrically corrected ("orthorectified") such that the scale is uniform: the photo or image follows a given map projection. Unlike an uncorrected aerial photograph, an orthophoto can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt.
A contour line 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 parallel to the -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.
A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features.
Planimetrics is the study of plane measurements, including angles, distances, and areas.
The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface . The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.
Terrain cartography or relief mapping is the depiction of the shape of the surface of the Earth on a map, using one or more of several techniques that have been developed. Terrain or relief is an essential aspect of physical geography, and as such its portrayal presents a central problem in cartographic design, and more recently geographic information systems and geovisualization.
A "quadrangle" is a topographic map produced by the United States Geological Survey (USGS) covering the United States. The maps are usually named after local physiographic features. The shorthand "quad" is also used, especially with the name of the map; for example, "the Ranger Creek, Texas quad". From approximately 1947-1992, the USGS produced the 7.5 minute series, with each map covering an area one-quarter of the older 15-minute quad series, which it replaced. A 7.5 minute quadrangle map covers an area of 49 to 70 square miles. Both map series were produced via photogrammetric analysis of aerial photography using stereoplotters supplemented by field surveys. These maps employ the 1927 North American Datum (NAD27); conversion or a change in settings is necessary when using a GPS which by default employ the WGS84 geodetic datum. Beginning in 2009, the USGS made available digital versions of 7.5 minute quadrangle maps based on GIS data that use the NAD83 datum, which is typically within one meter of WGS84, or within the uncertainty of most GPS coordinate measurements. On a quadrangle map, the north and south limits are not straight lines, but are actually curved to match Earth's lines of latitude on the standard projection. The east and west limits are usually not parallel as they match Earth's lines of longitude.
A stereoplotter uses stereo photographs to determine elevations. It has been the primary method to plot contour lines on topographic maps since the 1930s. Although the specific devices have advanced technologically, they are all based on the apparent change in position of a feature in the two stereo photographs.
An orienteering map is a map specially prepared for use in orienteering competitions. It is a topographic map with extra details to help the competitor navigate through the competition area.
Planetary cartography, or cartography of extraterrestrial objects (CEO), is the cartography of solid objects outside of the Earth. Planetary maps can show any spatially mapped characteristic for extraterrestrial surfaces.
A national mapping agency is an organisation, usually publicly owned, that produces topographic maps and geographic information of a country. Some national mapping agencies also deal with cadastral matters.
The Ethiopia-United States Mapping Mission, also known as the Ethi-U.S. Mapping Mission, was an operation undertaken by the United States Army during the 1960s to provide up-to-date topographic map coverage of the entire country of Ethiopia. The soldiers who conducted the mapping operations on the ground during that time used the latest surveying and mapping techniques and were exposed to many hardships and dangers, but they completed their mission near the end of the decade. The maps that were created still serve as the base maps for the country of Ethiopia and are presently being updated and maintained by the Ethiopian Mapping Authority.
The United States Geological Survey, abbreviated USGS and formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization's work spans the disciplines of biology, geography, geology, and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility.
The Army Map Service (AMS) was the military cartographic agency of the United States Department of Defense from 1941 to 1968, subordinated to the United States Army Corps of Engineers. On September 1, 1968, the AMS was redesignated the U.S. Army Topographic Command (USATC) and continued as an independent organization until January 1, 1972, when it was merged into the new Defense Mapping Agency (DMA) and redesignated as the DMA Topographic Center (DMATC). On October 1, 1996, DMA was folded into the National Imagery and Mapping Agency (NIMA), which was redesignated as the National Geospatial-Intelligence Agency (NGA) in 2003.
Major James Warren Bagley was an American aerial photographer, topographic engineer and inventor.