Finding the Best Route on a Topographic Map

Large-scale topographic mapInterpreting a topographic map for the purposes of planning a hike is essential for longer-distance or cross-country expeditions. In this article, learn some general approaches to orienting your upcoming trek.

Instructions

Difficulty: Moderately Easy

 
Things You’ll Need:
  • Large-scale topographic map (ex. USGS 1:24,000)
  • Map compass
 
Step 1
Picking the right cartographic representation of the country you're exploring is obviously essential. While topographic maps of smaller scale---with more area covered---are useful for general scouting of possible routes, you will need to consult a large-scale map, like the USGS 7.5-minute, 1:24,000-scale quadrangle series, which shows more detail, to plan your trip. In this series, which covers all the lower 48 states, Hawaii and U.S. territories, 1inch equals 2,000 feet.
The heart of a topographic map is the contour line, spaced at intervals depending on the severity of slope (the interval will be noted on the map). Closed contours define a summit---or, if hashed, a depression.
Step 2
Appraise the terrain you'll be dealing with after you've selected the appropriate map. Where are the highest points? These are designated by closed contour lines, and usually by an elevation; they'll often be useful landmarks to navigate and set bearings by in the field. Where are the drainages? Most streams carve V-shaped gorges (except those with glacier-scoured channels, which are distinctively U-shaped), the clustered, fanning contour lines of which stand out.
Step 3
Be kind to your knees: Choose a route with as little elevational change as possible, unless you're looking to scale a summit. Streams generally follow the path of least resistance, carving the lowest possible course across a landscape. Be aware, however, that especially in their upper reaches, drainages are steep and often choked with brush and rocks---the detritus of gravity and excavating water.
Step 4
Route long-distance treks via water sources. Along with obviously-marked lakes and rivers, look for the small blue circles that, on USGS maps, symbolize springs; you can often find them at the heads of creeks (at or near the base of the drainage's "V").
Step 5
Look for shelter. On USGS maps, green shading indicates forest cover. In mountainous country of sufficient elevation, the rock-heath mosaic above timberline can be an attractive cross-country travel alternative to the forested areas below. But it's good to be near such timber for the shelter it provides in the heavy heat of midday and afternoon, and during the lightning storms that render open areas so dangerous.
Step 6
Picture the terrain as you read the contour lines. A thick density trending from a divide suggests a steep slope; often, the gentler inclines are more favorable to foot travel. Sometimes the ridgeline itself, even if knife-edged, is the best route, especially in heavily-timbered areas; the tapering, jungled slopes on either side might be too obstructive.
Incorporate basic knowledge about vegetation patterns to get the most out of a topographic map. In most parts of the United States, north- and east-facing slopes, less exposed to direct sunlight, are likely to be more forested---and thus more challenging to cross---than their drier, south- and west-facing counterparts.
Step 7
Identify possible obstacles. The base and lower slopes of a scarp may be strewn with talus and scree (dislodged rocks). Floodplains of major rivers---quite obvious as broad flats surrounding a meandering channel---may be waterlogged or swampy. Speaking of which, marshes, swamps and bogs are symbolized on USGS maps---so plan your route accordingly.
An area of erratic slope and frequent small, closed contours often indicates landslide terrain. An older slide in country of otherwise steeply-dissected drainages might offer relatively easy passage; a newer one could be difficult to traverse, strewn with deadfall and shrub thickets.
Step 8
Learn how to set bearings with a map compass for putting your route-planning exercises to work in the field (see Resources).

Tips & Warnings

The route you set by topographic map ahead of getting out on the ground will necessarily require adjustment. The landscape may have changed since the map was last updated---due to such things as landslides, human development and flooding---and there will be plenty of unmapped obstacles to negotiate, like deadfall and thickets. Keep an open mind.
 
Realize when estimating travel time that more difficult terrain can add hours.
 
The USGS maps available on Trails.com can be cross-referenced with aerial photographs by selecting the desired setting on the map viewer.
 
Take the standard precautions for wilderness travel when you put your route-mapping exercises to practice. If you're taking the time to closely analyze a potential course on a large-scale map, you can be specific as to your probable whereabouts to family and friends prior to setting off.

Article Written By Ethan Schowalter-Hay

Ethan Schowalter-Hay is a writer and naturalist living in Oregon. He has written for the "Observer," the Bureau of Land Management and various online publishers. He holds a Bachelor of Science in wildlife ecology and a graduate certificate in geographic information systems from the University of Wisconsin.

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