Glossary

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This glossary is intended to help users of this site understand the relevant terms and expressions commonly used when ordering and using USGS maps. This glossary will be continually under construction as new definitions are added.

As always, if you have any questions or would like any further clarification of these or any other terms,
feel free to call us toll-free at (800) 627-0039 or e-mail us here.

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A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

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1:100,000 scale - The scale of the 30 x 60 minute (one degree by half a degree) Secondary Series of maps produced by the USGS. Covers a much greater area than a 1:24,000 scale map (covers an area equivalent to 32 7.5-minute maps), emphasizing major roads and cities. These quadrangles are available in standard topographic as well as BLM and mineral-management maps. These maps often use metric units.
1:1,000,000 scale - A scale sometimes used for the USGS State Map Series, essentially shrunken versions of the 1:500,000-scale maps without loss of information. State maps at this scale are only available in a planimetric format. (Note: The print on these maps is very small, so be advised to keep a magnifying glass at hand!)
1:24,000 scale - Refers to the 7.5-minute by 7.5-minute Primary Series of maps produced by the USGS. Commonly known for being equivalent to 1 inch=2000 feet.
1:25,000 scale - Some maps have been done at this scale to facilitate the use of metric units. Most of these are 7.5 x 15 minute maps which combine and usually supercede two 7.5-minute maps. These are commonly found in New England, New York, and some parts of California and Michigan. Some of the more populated regions of Alaska are mapped at this scale.
1:62,500 scale - The scale of a 15-minute quadrangle. Approximately 1 inch=1 mile.
1:63,360 scale - The scale used for quadrangle maps in Alaska. Exactly 1 inch=1 mile.
1:250,000 scale - The scale used for the 1 degree by 2 degree Regional Map Series produced by the USGS. Not recommended for hiking or orienteering. Best used for a broad regional overview.
1:500,000 scale - The scale used for the State Map Series produced by the USGS.
15-minute map - These maps were used for the USGS Primary Map Series from the 1890's through the 1950's, when they were replaced by the more detailed 7.5-minute series. They have a scale of 1:62,500 (roughly 1 in.=1 mi.) and cover an extent equivalent to four 7.5-minute maps. Though these maps have long been out-of-print, Map Express can obtain copies of older editions of these maps. See our Historic Topo Page for details.
30x60 minute map - Refers to the Secondary Map Series at 1:100,000-scale. Covers an extent of 1 degree by a half degree. In western states, these maps are usually also available in a BLM surface-management format. These maps always come pre-folded.
7.5-minute map - Refers to a Primary Map Series 7.5-minute, 1:24,000-scale quadrangle, generally the most detailed produced by the USGS. The term 7.5-minute itself refers to the geographic extent of these maps, each of which cover 7.5 minutes of latitude and 7.5 minutes of longitude. This map is usually what people refer to when they say "quad."
7.5 x 15-minute map - During the 1980's, the USGS replaced some of their 7.5-minute quadrangles with these 1:25,000 scale maps in an effort to convert to metric units. These pre-folded maps cover an extent equivalent to that of two 7.5-minute maps. Most of New England and much of New York are still only available in this series of maps, along with parts of California and small areas in other states. Many of these maps are already being phased out and returned to a more "traditional" 7.5-minute format, due to lack of public and professional enthusiasm for the metric conversion.

A

Aerial photograph - A photograph taken from an aircraft. See also: DOQQ, orthophoto, satellite photo.

B

Base map - A map on which additional information can be marked. USGS maps, being in the public domain, are often used as base maps for private map publishers, particularly publishers of hiking or recreational topo maps. Also sometimes used to refer to the planimetric State Series Maps.
Bathymetric - Showing underwater topography, including lake and river beds, and sea floors.
BLM map - A 1:100,000-scale 30x60-minute topographic map published by the Bureau of Land Management showing public land in various colors, while private land is white. These maps are available for most of the Western United States, having the same names and extent as their standard Secondary Series counterparts, and are updated much more frequently. Very popular with hunters.

C

Cartography - The art and science of creating maps.
Contour - A line of equal elevation, the most common method for showing topographic information on a map.
Contour map - (see Topographic map)
Contour interval - The difference in elevation between adjacent contours. For example, on a map with a contour interval of 10 feet, the ground rises or drops 10 feet with each successive contour. Contour intervals can vary greatly depending on scale and terrain. On most USGS maps, the contour interval is listed in the center of the bottom margin, above the scale bar.
Coordinates - A series of numbers describing a precise geographic location. There are many coordinate systems found on USGS maps, including traditional geographic coordinates, UTM coordinates, and state plane coordinates. Coordinates describing the latitude and longitude of a particular point are still the most common, and form the basis of the extent of USGS quadrangle maps.
Culture - On USGS maps, "culture" refers to any man-made feature above or below ground, including roads, cities, dams, sewers and radio towers.

D

Decimal Degrees - A description of geographic coordinates expressing latitude and longitude each as single numbers as opposed to a "degrees-minutes-seconds" reference, which uses a series of integers for each axis. (Example: 40.1425 latitude by -105.2675 longitude)
Declination (see Magnetic Declination)
Degree - 1/360 of a circle. When used in geographic coordinates, degrees are measured from the Equator and the Prime Meridian, going North, South, East and West. Degrees are further divided into minutes and seconds, or may be expressed in decimal degrees. Degrees are usually represented by the degree symbol (°).
Degrees-minutes-seconds - A description of geographic coordinates expressing latitude and longitude each as a series of three numbers: degrees, minutes, and seconds, as opposed to a "decimal degrees" reference, which uses single numbers for each axis. (Example: 40°08'22" N 105°15'45" W)
DEM - (Digital Elevation Model) A digital file, usually in raster form, describing the terrain and elevation of a given area, often of a particular USGS quadrangle. DEM's are mostly used in GIS applications.
DOQQ - (Digital Orthophoto Quarter-Quad) A digital raster image of an aerial photo mapped by the USGS, specifically a "quarter-quad," or the extent of one fourth of a 7.5-minute quadrangle, often used in GIS applications.
DRG - (Digital Raster Graphic) A scanned .tif image of a USGS quadrangle, paired with an accompanying .tfw (TIFF World File) which provides georeferencing information. Though often used for GIS projects, DRG's can be viewed by most image viewing software.

E

English units - Traditional American measurements, including miles, feet, inches, etc. Most USGS maps still use English units, though some scales (i.e. 1:100,000 and 1:25,000) are now using metric units.
Equator - A great circle line bisecting the Earth, equidistant from the poles, and used as the baseline for latitude measurement.
Extent - The geographical area a map covers. The extent of most USGS maps is defined by a uniform grid based on latitude and longitude.

F

Failed expedition - An expedition whose leader forgot to obtain the proper topographic maps from Map Express before starting out.

G

Geographic Coordinates - The traditional coordinate system based on latitude and longitude. Coordinates are measured using degrees, minutes, and seconds, measured angularly from the Earth's center from the Equator and the Prime Meridian. Latitude is measured from the Equator, while longitude is measured from the Prime Meridian.
GIS or Geographical Information Systems - The combination of maps with databases using computers. GIS is a rapidly emerging field, employed by corporations, the military, and all levels of government agencies.
GPS or Global Positioning System - A system of satellite and ground installations originally developed by the United States military to enable a user to determine their absolute location on the surface of the Earth. The satellites do not track individual GPS devices--rather, the device itself receives the signals from the satellites and triangulates its own position relative to their known positions. GPS can best be integrated with paper maps using the UTM coordinate system.
GQ or Geologic Quadrangle - A geologic map with an extent equivalent to a USGS quadrangle, usually at 1:24,000 or 1:250,000-scale.
Gradicule - The grid or tick marks representing geographic coordinates on a map.

H

Hazardous Journey - An adventure being attempted without the benefit of a map. Hazardous journeys can be avoided with the help of a topographic map from Map Express.

I

Index map - A map showing the location of all the USGS quadrangles in a given state. Map Express can provide free state indexes through the mail, or you may use our new online map index here.
International Date Line - The line, running mostly along 180° East/West longitude, to the east of which the calendar date is one day earlier than to the west.
Isoline - A line on a map which connects locations of equal value or distribution, commonly used as contours on a topographic map or on weather maps to show rainfall or temperature.

J

Jaguar - A large predatory jungle cat known to attack people not carrying topographic maps obtained from Map Express.

K

Karma - The total effect of a person's actions and conduct during the successive phases of the person's existence, regarded as determining the person's destiny. Good karma can be obtained by ordering your maps from Map Express.

L

Latitude - A measurement of degrees, minutes and seconds from the Equator, up to 90° North or South at the poles. A degree of latitude is equivalent to a nautical mile.
Longitude - A measurement of degrees, minutes and seconds from the Prime Meridian, up to 180° East or West at the International Date Line.

M

Magnetic Declination - The angular difference between observed magnetic North on a compass and geographic or "true" North. Magnetic declination is not constant--rather, it varies annually due to the "wandering" of the North Pole.
Meridian - Any line of longitude running between the poles. The Prime Meridian is used as the baseline for all longitude measurements.
Metric units - The international units of decimal measurement based on meters (i.e. centimeters and kilometers). USGS maps generally use English units, though most 1:100,000 and 1:25,000-scale quads do use metric units.
Mineral-management maps - Similar to surface-management BLM maps, these 1:100,000-scale maps show land ownership relating to mineral rights.
Minute - 1/60 of a degree.

N

Nautical Mile - A linear measurement of distance equivalent to one minute of latitude or approximately 1.15 miles. (Thanks to Pam for correcting my mistake)

O

Orthophoto - A satellite or aerial photograph that has been adjusted (or rectified to correct for natural distortions caused by the perspective of the aircraft or spacecraft that had taken the photo.

P

Parallel - A line circling the earth at a constant latitude. The Equator is the parallel at 0° latitude that serves as the baseline for all latitude measurements.
Planimetric - Showing only horizontal features, omitting topographic information.
Primary Map Series - The USGS series with the most detailed topographic map coverage for the United States. Maps are 7.5-minute quadrangles at 1:24,000-scale. Prior to the 1950's, the Primary Map Series consisted of 15-minute maps at 1:62,500-scale. There are over 50,000 7.5-minute maps covering the United States.
Prime Meridian - The baseline for all longitude measurements, a meridian running from the north to the south pole through the Royal Observatory in Greenwich, England.

Q

Quad (Quadrangle) - A map with a roughtly rectangular extent, defined by the four angles of its corners, which are often regularly spaced based on latitude and longitude. The term "quad" often simply refers to a 7.5-minute map.

R

Raised relief map - A map showing topography via an actual physical model of terrain. Most raised relief maps exaggerate elevation by at least a factor of 2.
Regional Map Series - The USGS series of 1:250,000-scale 1 degree by 2 degree topographic quadrangle maps.

S

Satellite photo - A photograph of the Earth's surface taken from a spacecraft in orbit.
Scale - The ratio between the size of features shown on a map and the physical reality which they represent. The scale on USGS maps is shown both via a scale bar and a numeric ratio. For example, if a map has a scale of 1:24,000, 1 inch on the map equals 24,000 inches on the Earth (2000 feet). Since there are 63,363 inches in a mile, a map with a scale of 1:63,360 is 1 inch=1 mile.
Scale bar - A bar included in the margin or legend of a map showing the relationship of distances on paper with those on the surface of the Earth. On USGS maps, the scale bar is generally in the center of the lower margin.
Second - 1/60 of a minute.
Secondary Map Series - The USGS series of 1:100,000-scale 30 by 60 minute topographic quadrangle maps.
Shaded relief map - A map showing (or suggesting) topography by simulating the shadows cast by hills and mountains. Generally, the "sun" in shaded-relief maps is in the northwest.
State Map Series - The USGS series of 1:500,000 and sometimes 1:1,000,000-scale maps for individual states. All state maps include counties, cities, major roads and highways, national forests and national parks. Most state maps come in topographic, shaded relief, and planimetric (base map) versions. The 1:1,000,000-scale maps are all planimetric. Larger states (i.e. Texas), only come in multiple 1:500,000-scale sheets.
State plane coordinate system - In states added to the Union after those in the original territory of the 13 colonies (Texas being a notable exception), the state plane coordinate system was developed for property ownership descriptions. Property descriptions include meridian, township, range, section and often sub-section identifiers.
Surface-management map - Usually a 1:100,000-scale topographic map produced by the Bureau of Land Managment (BLM) distinguishing public and private land. Public land is shaded with colors reflecting the agency or government that manages it, sometimes with special shading for specific uses or projects. These maps are generally only available in the Western United States, but they are updated much more frequently than their standard topographic counterparts produced by the USGS. Often simply referred to as a "BLM map," these folded maps are easily recognized by their golden-yellow covers.

T

Topo (see Topographic Map)
Topographic Map - A map showing elevation and the shape of the terrain (i.e. hills, peaks, and valleys) using raised-relief, shaded-relief, or contour lines.

U

USGS - The United States Geological Survey, originally chartered by the federal government in the 1870's to map the country using strict cartographic standards. The USGS publishes topographic, geologic and hydrologic maps, professional papers and bulletins, and mineral resource investigations. Map Express is the largest distributor of USGS maps and products.
UTM (Universal Transverse Mercator) - A metric rectangular coordinate system popular with GPS users. In the UTM system, the globe is divided into 60 zones, each of which is 6° of longitude wide, starting at the International Date Line and going east. UTM coordinates consist of the zone number, an "easting" (distance in meters or kilometers east of the western edge of the zone), and a "northing" (distance in meters or kilometers north of 80° south). In polar regions the UTM is replaced by its polar equivalent, the UPS system.

V

Vagabond - An individual who travels without a map. Vagabondism can be remedied by calling Map Express.

W

Wanderlust - A desire to travel. The first step in alleviating wanderlust is getting a map from Map Express.

X

Xebec - A small three-masted Mediterranean vessel with both square and lateen sails. One of the few words that starts with an "X."

Y

Yesterday - The day you needed your map. The next best thing is to order it from Map Express.

Z

Zen - A school of Mahayana Buddhism that asserts that enlightenment can be attained through meditation, self-contemplation, and the use of topographic maps from Map Express.