When I was learning how to read topographic maps, I developed a little memory heuristic to help remember the difference between contour lines that were going uphill versus those that were descending. I shared this with a hiker on one of my backpacking trips recently and it really helped them understand what the lines mean on a topographic map, so I thought I’d pass it along.
Let’s look at an example. This is a topographic representation of a hill. If you walk in the direction of the red arrow, you cross contour lines that are shaped like a frown, which frequently means you are going downhill.
Now, let’s look at a landscape and then a real map to demonstrate how to use this heuristic in practice.
This is Mount Lafayette in New Hampshire and here’s the topographic map for it from the National Geographic Topo DVD.
If you walk in the direction of the arrow, you will intersect contour lines that are shaped like a frown. While you’ll often be going downhill when this happens, you should still check the elevation markings (numbers) on the contour lines to see if they are descending or ascending, to be sure.
This is a case where you can descend from higher ground and not encounter a frown shaped contour line on a map. If you are descending into the head of a ravine, the contour lines won’t look like a frown but will be v-shaped. Take a look at this example below. This area is called Eagle Ravine and it’s a very steep avalanche zone on the northwestern shoulder of Mount Lafayette.
As you can see, the contour lines at the point of the V shape are very close together which indicates a steep elevation grade. If you trace the contour lines out from the point of the V you’ll see that they are frown shaped as they approach each other, although it’s a little harder to see their curve until you move father away from the point where they intersect.
This isn’t really a contradiction to the frown is down rule of thumb because there are downhill gradients (and frowns) on either side of the V, but it does highlight the care you need to take when interpreting contour lines that are flatter and less curved, when reading a topographic map.
Lakes and Valleys
If you’re standing at a low point in the landscape like a lake that is surrounded by hills, the frown is down heuristic doesn’t always work if you start walking uphill. Let’s look at East Pond, which is located just west of Mt Osceola in the White Mountains, for an example of this.
In this case, if you walk in the direction of the arrow, you will be crossing frowns but going uphill. You can determine this because the 3000 foot contour line is outside or beyond the 2800 foot contour, indicating an ascent if you walk in that direction.
Here’s what East Pond looks like, to help you match the symbols on the map to the actual landscape. As you can see, the landscape forms a saddle between two high points. The best advice I have to give in situations like these is to be sure to check the contour elevations when reading your map, to double check your interpretation of the topographic map you’re using.