Reading Topography On A Map

Maps are great and completely save your bacon. They can also be treacherous. In fact, the selfsame map can either provide a wealth of information or encourage all sorts of false conclusions about routes and travel times. The difference lies in your skill in reading topography from a map.

So what can be treacherous about a map? Well, we all know that so much distance on the map means so much distance on the ground. Maps have keys that give the conversion. We also have some notion of how fast we walk. Those combine to a notion of how long it will take us to walk an inch of map distance.

And that idea is Way Wrong if the topography is challenging and you didn’t account for it.

It can also be flatly impossible to walk from Point A to Point B seen on a map if the real world has nasty topography between them. 

Topographic maps that directly show contour

The easiest to use topographic maps are those that show the relief in colors, in a way that looks 3-D to our eyes.

Relief maps are colored to encourage our brains to ‘see’ the 3D terrain.(1)

Relief maps have the strong upside of being intuitive. That means we’re less likely to misinterpret them even when tired, stressed, and distracted. They have the downside of being less detailed and specific than contour line maps.

The most detailed information comes from contour line maps

This is the kind of topographic map the US Geological Survey produces. By they way, you can download these USGS maps of anywhere in the U.S., already paid for through tax dollars; or buy paper copies. The link above will take you there.

These topographic maps rely on the key concept that each contour line represents a single elevation. On a related note, the elevation difference between adjacent lines stays the same, too. Once you get some practice with them, your mind will construct a 3D image from the contour lines. Until that happens, some rules will help.

Each contour line is one elevation. Close together contour lines mean steep slopes.

Topographic interpretation rules for contour line maps

• Traveling along a contour line is flat. Going perpendicular to a contour line means you’re going directly up or down a slope. 
• When contour lines are close together, the slope is steep. (On a related note, when the lines lie on top of one another, such as at a cliff face, you have to be careful not to lose track of how tall the cliff is/how many lines.)
• Concentric rings of contour lines are hills or valleys. 
• Tall points usually have elevations marked at the top.
• Gentle valleys draw a pattern of U shapes. Sharp valleys or gullies draw V patterns. These all point uphill.
• Gentle ridges or spurs also draw U patterns and sharper ridges and spurs dray V patterns. Ridge and spur patterns point downhill though.
• If you have trouble telling uphill from downhill Us and Vs …. if there’s a watercourse in the middle of it, it’s a valley or gully. If there’s an elevation marker at the heart of it, it’s a ridge or spur.
• Saddles or passes look like hourglasses.

Please keep in mind too that terrain significant to a person on foot may still not show up on a contour map. For example, The Place has a creek that has eroded itself a ten foot straight drop-off of a channel. It wouldn’t show up on any contour map whose interval line is more than ten feet, but it’s still a bear to crawl down then up to cross.

Topography from a road map

Road maps are often not kind enough to offer either relief coloring or contour lines. That makes judging topography harder. There are some clues though.

• Are you prepared for a shock? Water is found in low places. Roads that follow watercourses are in river valleys, unless you’re in seriously mountainous country full of waterfalls.
• Watercourses with lots of slow, lazy curves are usually running through flat land. Watercourses with sharp, abrupt curves usually just ran into a cliff or other dramatic terrain.
• Flat land usually has straight roads.
• Lots of dogleg curves in a road usually means steep slopes.
• Less aggressive but frequent changes in direction of roads are common in hilly areas. Many of those roads are following ridge lines, which minimizes the amount of ups and downs. Love me some ridge roads!
• Lots of small areas of water scattered around means low, flat, swampy ground.

Pro tip: Don’t trust terrain advice from drivers

This one I learned as a cyclist. To a cyclist, or a walker, terrain is a big hairy deal. Hills can suck your will to live after a while. So topography is a matter of interest.

But don’t bother trying to find out by asking someone who’s only done the route in motorized vehicles. They might accidentally have noticed accurately — but they’re Way worse at it than you’d imagine. What seems “pretty flat” when 450 horses are hauling your hindquarters around does not necessarily feel pretty flat when you’re self-powered. (Not that I’m bitter…)

p.s. For more on finding your way with map and compass, click here and here.

Thanks for the images

1) © Sémhur / Wikimedia Commons / CC-BY-SA-3.0, or Free Art License