Topographic Maps 101
by Will Robertson
The intricate details on a topographic
map can be befuddling, even frustrating, if you are learning
while out in the backcountry. But once you get familiar with
the markings and symbols, reading maps will become a friendly
aid, rather than a dreaded assignment.
Topographic Maps Grid System
Lines of latitude run parallel to the
equator (east and west), and lines of longitude run perpendicular
to the equator (north and south). These lines form a pattern
of squares across the surface of the earth like a checker board.
One square, formed by lines of longitude
and latitude, measures 90 degrees x 90 degrees. Degrees are further
subdivided into minutes and seconds.
• 1 degree = 60 minutes
• 1 minute = 60 seconds
The important thing to understand, when
we look for a topographic map for our hiking adventures, is that
it will be located within this larger context of degrees, minutes,
and seconds. Fortunately, it will also, usually, be identified
with a place name.
An alternative method of notation within
the Geographic Coordinate System is the decimal degree system.
In the decimal degree system, minutes and seconds are replaced
by a percentage of a degree, expressed as a decimal up to four
places long. It is often used for Geographic Information Systems
(GIS) applications,
Topographic Maps Scale Explained
A topographic map lists its scale in
the margin or legend. The scale is the relationship between distances
on a map and the corresponding distance on the ground. For example,
a map with a scale of 1:50,000 means that 1 unit of measurement
on the map equals 50,000 equivalent units on the ground.
Units can be in inches, feet, centimeters,
or meters, depending on what scale map you are looking at and
what measuring system the country uses. Most USGS maps are 1:24,000,
also known as 7 ½ minute maps. On this map, 1 inch = 24,000
inches on the ground. In Canada, most hiking maps are 1:50,000
scale, where 1 cm = 50,000 cm on the ground.
A small scale map (ex. 1:100,000) covers
a large area; it shows less detail with fewer features. A large
scale map (ex. 1:10,000) covers a small area; it shows great
detail and small features. A 1:2,500, large scale map would show
individual houses and street lights.
Topographic Maps Symbols and
Colors
The symbols and colors used on Topographic
maps are fairly straight forward:
• Black - man-made, “cultural,”
features such as roads, buildings, etc. It is also used to show
geographical names (toponymy), certain symbols, geographic coordinates,
precise elevations, border information and surround information.
• Blue –water, lakes, rivers,
streams, etc. The names of bodies of water and water courses
are also shown in blue, as are magnetic declination and UTM (Universal
Transverse Mercator) grid information.
• Brown - contour lines, contour
elevations, spot elevations, sand.
• Green - areas with substantial
vegetation like a forest, orchard, or vineyard
• Grey - used on the back of the
map where the different symbols and a glossary of terms and abbreviations
can be found.
• Orange - unpaved roads and unclassified
roads and streets.
• Purple - features added to the
map since the original survey. These features are based on aerial
photographs but have not been checked on land.
• Red - major highways; boundaries
of public land areas. A red tint is used to show an urban development.
• White - areas with little or no
vegetation; also used to depict permanent snowfields and glaciers
Topographic Maps Glossary
• Bearing - Angular direction expressed
in degrees.
• Contour Lines – A line on
a map joining points of equal elevation. These lines are used
to illustrate relief on a map.
• Distortion - The difference in
shape between the actual curved surface of the earth and the
flat representation of a topographic map.
• Grid - A system of horizontal
and vertical lines that provide coordinates for locating points
on an image.
• Magnetic Declination - The angle
between magnetic north and true north, expressed in degrees and
minutes, east or west from true north.
• Magnetic North - The direction
your compass needle points.
• Projection - A method by which
the curved shape of the earth is represented on a flat surface,
overcoming distortion.
• Relief – The variations in
elevation of the earth’s surface.
• Scale – The relationship
between distance on a map and the corresponding distance on the
ground. For example, a map with a scale of 1:50,000 means that
1 unit of measurement on the map equals 50,000 equivalent units
on the ground.
• Topographic Map – An illustration
of the earth’s different elevation levels by means of contour
lines. They present both natural and manmade features.
• True North - Direction of the
northern rotational axis of the earth – the North Pole.
About the Author
Outdoors Adventurer, Writer and Webmaster
Will Robertson lives with his family in Little Rock, Arkansas.
Explore the best hiking vacations and
gear on the planet at:
http://www.hiking-vacations-and-gear.com
Note:
Link not working - if you are the author please contact me.
You can also read an article here on Magnetic Declination.
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