A Guide to USGS Topographic Maps (with Symbol Key)

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What is a Topographic Map?

A map is a representation of the Earth, or part of it. The distinctive characteristic of a topographic map is that the shape of the Earth’s surface is shown by contour lines. Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface, such as mean sea level. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes. A topographic map shows more than contours. The map includes symbols that represent such features as streets, buildings, streams, and vegetation. These symbols are constantly refined to better relate to the features they represent, improve the appearance or readability of the map, or reduce production costs. Consequently, within the same series, maps may have slightly different symbols for the same feature. Examples of symbols that have changed include built-up areas, roads, intermittent drainage, and some lettering styles. On one type of large-scale topographic map, called provisional, some symbols and lettering are hand-drawn. Contour maps, while sill maintained by the USGS, are becoming a thing of the past. New presentation of topographic data, enhanced by information from satellites can now be mapped digitally. Google’s own terrain maps, while not nearly as detailed as the USGS contour maps, do away with highly detailed contour lines, and opt for a 3D-like shading system to illustrate elevation. But the principle remains the same: these types of maps are for illustrating elevation of land. While readily available online, the new shaded topographic maps are rarely found printed as hard copy. In the disconnected wilderness, contour maps still reign supreme.

Reading Topographic Maps

A small piece of topographic map

The contours show elevation differences. Labeled index lines (thick) and intermediate lines (thin) allow for approximations of height at a given point. The shaped groups of contours represent hills, valleys, gullies and level land. The contours above illustrate a hill with a 245 meter high summit.

Interpreting the colored lines, areas, and other symbols is the first step in using topographic maps. Features are shown as points, lines, or areas, depending on their size and extent. For example, individual houses may be shown as small black squares. For larger buildings, the actual shapes are mapped. In densely built-up areas, most individual buildings are omitted and an area tint is shown. On some maps, post offices, churches, city halls, and other landmark buildings are shown within the tinted area. The first features usually noticed on a topographic map are the area features, such as vegetation (green), water (blue), and densely built-up areas (gray or red). Many features are shown by lines that may be straight, curved, solid, dashed, dotted, or in any combination. The colors of the lines usually indicate similar classes of information: topographic contours (brown); lakes, streams, irrigation ditches, and other hydrographic features (blue); land grids and important roads (red); and other roads and trails, railroads, boundaries, and other cultural features (black). At one time, purple was used as a revision color to show all feature changes. Currently, purple is not used in revisions, but purple features are still present on many existing maps. Various point symbols are used to depict features such as buildings, campgrounds, springs, water tanks, mines, survey control points, and wells. Names of places and features are shown in a color corresponding to the type of feature. Many features are identified by labels, such as “Substation” or “Golf Course.” Topographic contours are shown in brown by lines of different widths. Each contour is a line of equal elevation; therefore, contours never cross. They show the general shape of the terrain. To help the user determine elevations, index contours are wider. Elevation values are printed in several places along these lines. The narrower intermediate and supplementary contours found between the index contours help to show more details of the land surface shape. Contours that are very close together represent steep slopes. Widely spaced contours or an absence of contours means that the ground slope is relatively level. The elevation difference between adjacent contour lines, called the contour interval, is selected to best show the general shape of the terrain. A map of a relatively flat area may have a contour interval of 10 feet or less. Maps in mountainous areas may have contour intervals of 100 feet or more. The contour interval is printed in the margin of each U.S. Geological Survey (USGS) map. Bathymetric contours are shown in blue or black, depending on their location. They show the shape and slope of the ocean bottom surface. The bathymetric contour interval may vary on each map and is explained in the map margin.

Key to Topographic Map Symbols

Boundaries

National
State or territorial
County or equivalent
Civil township or equivalent
Incorporated city or equivalent
Federally administered park, reservation, or monument (external)
Federally administered park, reservation, or monument (internal)
State forest, park, reservation, or monument and large county park
Forest Service administrative area*
Forest Service ranger district*
National Forest System land status, Forest Service lands*
National Forest System land status, non-Forest Service lands*
Small park (county or city)

Buildings and Related Features

Athletic field
Building
School; house of worship
Built-up area
Forest headquarters*
Ranger district office*
Guard station or work center*
Racetrack or raceway
Airport, paved landing strip, runway, taxiway, or apron
Gaging station
Located or landmark object (feature as labeled)
Covered reservoir
Boat ramp or boat access*
Unpaved landing strip
Well (other than water), windmill or wind generator
Tanks
Roadside park or rest area
Campground
Picnic area
Winter recreation area*
Cemetery

Roads and Related Features

Please note: Roads on Provisional-edition maps are not classified as primary, secondary, or light duty. These roads are all classified as improved roads and are symbolized the same as light duty roads.
Primary highway
Secondary highway
Light duty road, Light duty road, paved*, Light duty road, gravel*, Light duty road, dirt*, Light duty road, unspecified*
Unimproved road, Unimproved road*
4WD road, 4WD road*
Trail
Highway or road with median strip
Highway or road under construction
Highway or road underpass; overpass
Highway or road bridge; drawbridge
Highway or road tunnel
Road block, berm, or barrier*
Gate on road*
Trailhead*

Railroads and Related Features

Standard guage railroad, single track
Standard guage railroad, multiple track
Narrow guage railroad, single track
Narrow guage railroad, multiple track
Railroad siding
Railroad in highway, Railroad in road, Railroad in light duty road*
Railroad underpass; overpass
Railroad bridge; drawbridge
Railroad tunnel
Railroad yard
Railroad turntable; roundhouse

Transmission Lines and Pipelines

Power transmission line; pole; tower
Telephone line
Aboveground pipeline
Underground pipeline

Mines and Caves

Quarry or open pit mine
Gravel, sand, clay, or borrow pit
Mine tunnel or cave entrance
Mine shaft
Prospect
Tailings
Mine dump
Former disposal site or mine

Projection and Grids

Neatline
Graticule tick
Graticule intersection
Datum shift tick
State plane coordinate systems
Primary zone tick
Secondary zone tick
Tertiary zone tick
Quaternary zone tick
Quintary zone tick
Universal transverse metcator grid
UTM grid (full grid)
  UTM grid ticks*

Glaciers and Permanent Snowfields

Contours and limits
Formlines
Glacial advance
Glacial retreat


Contours

Topographic
Index (number indicates elevation above sea level)
    Approximate or indefinite
Intermediate
    Approximate or indefinite
Supplementary
Depression
Cut
Fill
Continental divide
Bathymetric
Index***
Intermediate***
Index primary***
Primary***
  Supplementary***

Bathymetric Features

Area exposed at mean low tide; sounding datum line***
Channel***
Sunken rock***

Rivers, Lakes and Canals

Perennial stream
Perennial river
Intermittent stream
Intermittent river
Disappearing stream
Falls, small
Falls, large
Rapids, large
Rapids, small
Masonry dam
Dam with lock
Dam carrying road
Perennial lake/pond
Intermittent lake/pond
Dry lake/pond
Wide wash
Narrow wash
Canal, flume, or aqueduct with lock
Elevated aqueduct, flume, or conduit
Aqueduct tunnel
Water well, geyser, fumarole, or mud pot
Spring or seep

Submerged Areas and Bogs

Marsh or swamp
Submerged marsh or swamp
Wooded marsh or swamp
Submerged wooded marsh or swamp
Land subject to inundation

Marine Shorelines

Shoreline
Apparent (edge of vegetation)***
Indefinite or unsurveyed

Coastal Areas

Foreshore flat
Coral or rock reef
Rock, bare or awash; dangerous to navigation
Group of rocks, bare or awash
Breakwater, pier, jetty, or wharf
Seawall
Exposed wreck
Depth curve; sounding
Oil or gas well; platform

Surface Features

Levee
Sand or mud
Disturbed surface
Gravel beach or glacial moraine
Tailings pond

Vegetation

Woodland
Shrubland
Orchard
Vineyard
Mangrove

Control Data and Monuments

Principal point**
U.S. mineral or location monument
River mileage marker
Boundary monument
Third-order or better elevation, with tablet
Third-order or better elevation, recoverable mark, no tablet
With number and elevation
Horizontal control
Third-order or better, permanent mark
With third-order or better elevation
With checked spot elevation
Coincident with found section corner
Unmonumented**
Vertical control
Third-order or better elevation, with tablet
Third-order or better elevation, recoverable mark, no tablet
Bench mark coincident with found section corner
Spot elevation


* USGS-USDA Forest Service Single-Edition Quadrangle maps only.
In August 1993, the U.S. Geological Survey and the U.S. Department of Agriculture’s Forest Service signed an Interagency Agreement to begin a single-edition joint mapping program. This agreement established the coordination for producing and maintaining single-edition primary series topographic maps for quadrangles containing National Forest System lands. The joint mapping program eliminates duplication of effort by the agencies and results in a more frequent revision cycle for quadrangles containing National Forests. Maps are revised on the basis of jointly developed standards and contain normal features mapped by the USGS, as well as additional features required for efficient management of National Forest System lands. Single edition maps look slightly different but meet the content, accuracy, and quality criteria of other USGS products.

** Provisional-Edition maps only. Provisional-edition maps were established to expedite completion of the remaining large-scale topographic quadrangles of the conterminous United States. They contain essentially the same level of information as the standard series maps. This series can be easily recognized by the title “Provisional Edition” in the lower right-hand corner.

*** Topographic Bathymetric maps only.

For more information about topographic maps produced by the USGS, please call: 1-888-ASK-USGS or visit us at http://ask.usgs.gov

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