TEX Dictionary
From NatGeoMaps
7.5-minute quadrangle - a 1:24,000-scale topographic map that shows an area that spans 7.5 minutes of latitude and 7.5 minutes of longitude, and it is usually named after the most prominent feature in the quadrangle.
Bearing - the direction from your current position to your destination
Compass rose - a symbol on a compass or map that is circular with graded points for the directions
Contour lines - isolines that show equal elevation on a map at defined intervals
Datum shift - this shift occurs due to the change in shape of the spheroid used to define the datum. This NAD shift amounts to about 210 meters for the conterminous United States.
Declination - A measurement of the degree to which a grid or magnetic north varies from true north. Declination is usually measured in mils, where one mil is equal to 1/6,400 of 360 degrees
Digital Elevation Model (DEM) -a set of data of regularly spaced elevation values based on horizontal geographic coordinates.
Digital Raster Graphic (DRG) - An electronic map that is based a scanned graphic image that has it pixel coordinate values converted to geographic coordinate values. DRG’s are scanned at 250 dpi and are stored as a TIFF file format.
Game Management Units (GMUs) - are defined areas determined by state wildlife agencies to effectively manage and control hunting. Each year, big-game hunters are assigned a particular unit to hunt within. This process helps control species population and ensures a great and safe hunting experience. Boundaries for Game Management Units often follow rivers, major highways, or other natural boundaries but can be challenging to follow in rugged terrain.
Geocaching - a type of scavenger hunt for waterproof containers bearing treasure using the containers' exact geographic coordinates and Global Positioning System devices
Graticules - a network of lines on a map which represent the meridians of longitude and parallels of latitude.
Greenwich Mean Time (GMT) - the time as measured from Greenwich England or 0 degrees Longitude.
Grid North - North according to the grid imposed on the map. Since grids ignore the curvature of the Earth, this is not the same as true north.
Grid - a network of uniformly spaced lines on the face of a map, intersecting at right angles and usually running north-south and east-west. Grids are often numbered and can be used to define position by rectangular coordinates.
Heading - your current direction of travel
Index map - a map that accompanies a map set that shows the overall arrangment of maps in the set, showing their numbering scheme and areas of coverage. It is useful for finding the particular map needed without having to browse through the entire map set.
Latitude - the angular distance north or south from the equator of a point on the earth's surface, measured on the meridian of the point.
Longitude - angular distance east or west on the earth's surface, measured by the angle contained between the meridian of a particular place and some prime meridian, as that of Greenwich, England, and expressed either in degrees or by some corresponding difference in time.
Magnetic Declination - the angle between magnetic north and true north at a particular location. Also called magnetic variation.
Magnetic North - North according to the Earth's magnetic poles rather than its geographic poles. Declination from true north is given in miles where one mile equals 1/6,400 of 360 degrees
Map credit – is the equivalent of one SuperQuad and costs $1
Map Datum - the two most important horizontal datums in the US are NAD27 and WGS84/NAD83. An elliptical model (spheroid) of the Earth that is used to measure both horizontal and vertical coordinates.
Map key (aka map legend) - explanatory table of symbols used on a map or chart
Meridian - A starting point/line, usually a line of longitude, for a numbering system to section the earth into a grid
Military Grid Reference System (MGRS) - is the geocoordinate standard used by NATO militaries for locating points on the earth. In most areas (between latitudes 80°S and 84°N), the MGRS grid is identical to the UTM (Universal Transverse Mercator) grid system, but uses a different labeling convention. In the polar regions, MGRS is based on the Universal Polar Stereographic system. MGRS grid reference does not describe a point on the earth's surface, but rather a square area of 10km x 10km, 1km x 1km, 100m x 100m, 10m x 10m or 1m x 1m, depending on the precision of the coordinates provided.
NAD 27 - North American Datum of 1927 based on the Clarke 1866 spheroid. Used as the datum on most large scale USGS quads.
NAD 83 - North American Datum of 1983 based on the GRS 80 spheroid. A newer version of the NAD datum, used on some of the newer versions of the large scale USGS quads. Almost identical to the WGS84 datum.
Prime Meridian - the meridian running through Greenwich, England, from which longitude east and west is reckoned
Projection - a way of depicting the three-dimensional surface of the Earth onto a two-dimensional sheet of map paper. There are many types of projections all of which aim to have the least amount of distortion on as many properties of the map as possible, such as distance, angular measurement, area, or shape
Raster Graphic Map - A software map that is generated using digital scans of paper maps.
Route – a series of sequential waypoints
SuperQuad - a new online set of maps by National Geographic Maps that consists of 7 layers and has the equivalent map coverage area of a 7.5-minute quadrangle by the USGS. SuperQuads are purchased from the online TOPO! Explorer Map Store. A SuperQuad costs $1 and is the equivalent to 1 map credit.
A SuperQuad's 7 layers:
Index map of the United States - *default starting layer
1. National Geographic Atlas Map 1:8,000,000 scale
2. National Geographic Atlas Map 1:2,000,000 scale
3. USGS 1:500,000 scale
4. USGS 1:100,000 scale
5. USGS 1:24,000 scale
6. I-Cubed aerial imagery
7. Hybrid - a blend of topographic and aerial imagery
Support Wiki – is an online instructional resource for TOPO! Explorer and TOPO! software applications produced by National Geographic Maps.
topo.com - hosts National Geographic's new National Recreation Database. Users can browse, download, and share updated trails to the website
TOPO! Explorer desktop application – the application allows users to download purchased SuperQuads (maps) and free trails to their computer(s). Users can also post their own trips, photos, and videos to the sharing community using the desktop application.
.tpo file - created by the TOPO! desktop software applications, versions 2.0 thru 4.x. These files can be imported into the TOPO! Explorer desktop application via the 'File - Open' menu in the Navigation Bar.
Track log (aka tracks) - are points automatically stored when you are moving. It is the electronic equivalent of laying down a "breadcrumb trail" to mark your path.
.trp file (aka trip file)- created by the TOPO! Explorer desktop application. Currently, there is no support for importing or exporting these trip files, but we plan to add such support to TOPO! Explorer in the near future.
True North - the direction of the geographical North Pole from a given point
Universal Polar Sterographic Grid (UPS) - A grid system that is similar to UTM and is used above 84 degrees North Latitude (Arctic) and below 80 South Latitude (Antarctic).
Universal Time Coordinated (UTC TC ) - GPS time as maintained by the satellites and converted to UTC time by the GPS receiver, basically Greenwich Mean Time. UTC time can be converted into Standard time by using the correct UTC offset in your GPS receiver.
Universal Transverse Mercator (UTM) coordinate system - is an international plane (rectangular) coordinate system developed by the U.S. Army. The UTM divides the world into 60 zones of 6 degrees longitude. Each zone extends 3 degrees east and west from its central meridian and are numbered consecutively west to east from the 180-degree meridian. Transverse Mercator projections may then be applied to each zone.
Vector Graphic Map - A software map in which all features (roads, rivers, topographic contours) are stored as a series of straight lines (vectors).
Waypoint - a reference point in physical space used for purposes of navigation. It can be a point on a route or track.
WGS84 - World Geodetic System of 1984, the default datum for GPS units. Almost identical to the NAD83 datum.
Wide Area Augmentation System (WAAS) - A method to improve the accuracy of civilian GPS units. It uses additional satellites as well as 25 ground stations to measure GPS errors and broadcast these corrections to WAAS enabled GPS units. There are currently two geostationary WAAS satellites located over the Pacific and Atlantic oceans.
