USING A MAP
Simple trail maps, the line-drawing variety often found in guidebooks,
are useful for trip planning but NOT for navigation in the field. To safely
find your way in wilderness terrain, you need the detail provided by
topographic maps. A map (together with a compass) is one of the Ten
Essentials in Scouting.
So know your maps:
Basic (planimetric) maps:
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Examples: Traditional road maps; hand-sketched
trail maps provided in visitor-center handouts.
Appearance: Flat, 2-dimensional, horizontal view of
land areas showing roads, rivers and trails.
Attributes: They display points of interest (viewpoints, trail junctions)
and routes that connect them, but offer no perspective on elevation
variances. Thus they may make the distance to your destination
appear to be modest, but they will not indicate if a deep valley or high
ridge must be crossed in order to reach it.
Usage: OK for following a simple nature trail or making a short trip on
a well-defined trail system, but insufficient for navigation should you
head deep into the wilderness or step off an established path.
Topographic (topo) maps:
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Examples: U.S. Geological Survey (USGS)
quadrangles; customized commercial and
downloadable map products.
Appearance: Areas of varying colors (or shades of
gray) are overlaid with "squiggly" contour lines.
Together they combine to give trained eyes a mental picture of the
elevation variances in a landscape. Tightly spaced contour lines, for
example, indicate steeper terrain.
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Attributes: Their ability to convey the physical relief (the highs and
lows) of a landscape enables you to orient yourself in the field by
identifying prominent natural features—peaks, ridgelines or valleys.
They also show the location of prominent man-made features such as
roads and towns.
Usage: Always the best choice for any type of wilderness travel, from
day trips to extended expeditions. Even if you're hiking on what you
believe is an established, well-signed, can't-get-lost trail system, a
topo map remains a helpful tool when you reach a viewpoint and
want to identify peaks and landmarks with certainty.
How Do Topo Maps Describe the Terrain?
Contour lines: They connect points on the map that share the same
elevation, providing a 3-dimensional perspective of the landscape.
Tightly packed contour lines indicate steep terrain; widely spaced lines
indicate relatively level terrain. Contour lines never intersect.
Contour interval: Contour lines are separated at specific elevation
intervals. Intervals may vary by individual map, appearing every 20, 40,
80, 100 or 200 feet. But the interval used on a single map (say, 80 feet)
remains consistent throughout that map. A map's chosen contour
interval is identified in the margin of each map.
Index contour lines: Every fifth contour line is the index contour line.
Usually the line is slightly bolder and intermittently includes the
elevation (usually the number of feet above sea level) of all points on
that line.
Scale: Beyond the ratio scale (described later in this article), a map
includes a horizontal graphic scale. It displays how a measurement on
the map (1 inch, for example) equates to miles/kilometers of terrain
covered by the map.
Colors and shading: Darker colors (or shades of gray) represent dense
vegetation. Lighter colors (particularly greens) or shades of gray
indicate comparatively sparse vegetation. Lighter colors (such as beige)
or no colors suggest open terrain. White spaces with blue edges
indicate permanent snowfields or glaciers.
Magnetic declination diagram: Printed in the margin of the map, this
diagram shows the difference (declination) between magnetic north
(indicated by the MN symbol) and true north (or polar north, indicated
by a star symbol).
Grid: Numbers displayed around the edge of a map represent two grid
systems that can be used to determine your location.
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Latitude and longitude: Exact L&L numbers are displayed in the
corners of maps and at equal intervals between the corners.
Universal Transverse Mercator (UTM): This system, used primarily by
the military, divides the earth's surface into a number of zones.
Combined, all of the above can enable you to determine your elevation,
the ruggedness of the terrain around you and the most desirable route
to travel to reach a destination.
Choosing a Topo Map
Two factors play a role when you evaluate maps: Scale and content.
Scale
A map's ratio scale conveys the relationship between a measurement
on the map and the distance it represents on the terrain. The most
popular USGS maps offer a scale of 1:24,000, which means 1 inch (or
foot, or any unit of measure) on the map represents 24,000 inches on
the ground.
Mapping software makes it possible to create customized maps that
offer a larger scale (say, 1:12,000 or lower) to provide greater detail.
Customized commercial maps are also sometimes created at these
larger scales. This is especially useful for off-trail explorers who want to
choose passageways through saddles or passes that offer the least
resistance.
The downside: Such maps cover a small area. People who undertake 1way, multiday trips along a linear route often choose small-scale maps
(1:50,000 or 1:62,500, for example). These maps cover a lot of land
area but offer less detail. When terrain becomes very steep, contour
lines runs so closely together that they appear almost as blobs rather
than lines.
So if you're a long-distance traveler, a small-scale map will give you a
good overview of the territory you're exploring (much as a road map
does). The good news: You don't have to carry a dozen or so maps to
cover your trip. But if you decide to go off-trail in a certain area, all a
small-scale map may offer you is a clot of tiny, tightly packed lines—
likely not enough detail to make wise navigational decisions.
Note: The terms "small-scale" and "large-scale" can be confusing to
beginners since ratios get smaller as their denominators get larger.
Remember this: 1:24,000 is a larger scale than 1:250,000, since the
fraction 1/24,000 is larger than 1/250,000.
Content
Some commercial (non-USGS) maps include additional features that can
be valuable to some users. They include:
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Highlighted trails
Elevation call-outs
Distances between trail junctions and landmarks
Primitive trails
Backcountry campsites
Springs
Highlighted boundary lines
These additions, even GPS coordinates and personal notations, can be
inserted onto maps when created using mapping software.
Map Options
USGS Quadrangles
The USGS is the major supplier of topographic maps in the United
States. USGS maps cover rectangular areas of land called quadrangles.
The borders of these maps are determined by latitude lines, longitude
lines and the smaller divisions between them (minutes). Every square
mile of the U.S. is covered by USGS maps, and each map lines up flush
with the others around it.
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Pros: USGS quads are available locally at most REI stores. They are
easy to use and easy to fit together when your trail crosses over onto
an adjacent map (the borders match exactly, and the titles of
adjacent maps are printed on the borders of each map).
Cons: They typically provide limited trail information. Plus their
information is sometimes dated. It's not uncommon to find that the
location, even the existence, of roads, bridges, trails and shorelines
have changed since the map was printed.
Commercial Maps
Private map companies sometimes enhance existing topographic maps
with highlighted features or, more commonly, create customized maps
that focus on popular areas that attract lots of visitation (and therefore
potential customers).
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Pros: Such maps not only have key features (primarily trails)
highlighted, they are updated regularly. Release dates are usually
found near the scale or the magnetic declination diagram.
Cons: Higher cost; some remote yet scenically worthwhile areas are
not covered by such maps.
Mapping Software
This is an exciting, ever-evolving category of products that allows
computer-savvy adventurers to create customized maps. Choose a
scale that best suits your needs, insert notes and reminders, toss in GPS
coordinates, print it at home on waterproof paper. Nice.
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Pros: It's hard to beat a map customized to the exact scope of your
trip.
Cons: Higher initial cost; some degree of computer sophistication is
required.
Local Maps
Many government-owned public lands (national parks, national forests,
state parks, recreational areas) produce their own maps to cover the
land inside their boundaries. Some are free handouts (but usually
planimetric). Some handouts focus on a specific trail.
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Pros: An entire park or area is encompassed on a single map, usually
with information about roads, attractions and trails. Some get regular
updates.
Cons: If they are topographic, they usually are small-scale (meaning
minimal detail), and they can be expensive.