Reading topographic maps is essential to understand the geography of new areas and to better prepare for wilderness outings.
Reading Topographic Maps
The issue with traditional maps is that they are 2D, or flat, while the earth and it's terrain is not. Topographic maps allow a two-dimensional map to represent a three-dimensional earth, thereby providing you with valuable recon to help you plan your navigation.
These maps represent elevation through a series of contour lines. Each contour line represents a specific elevation, and the line connects all the points, that are the same elevation, in this area. These lines are indicated as brown on a topographic map, with index lines shown in heavier brown.
Contour lines and Index Line (Darker Brown and labeled "900")
Elevation values are labeled along the index line and indicate the feet above sea-level. The contour lines between index lines evenly divide the elevation change – for example, if there were five lines demonstrating a gain of 100 feet, each contour line would indicate a gain of 20 feet.
5 lines between 900ft elevation and 1000ft elevation, therefore each line is equal to a 20 foot increase in elevation.
To effectively use a topographic map, you need to understand what the lines mean, in relation to the area’s topography. The spacing of the contour lines indicates the slope or rise of the ground.
Lines that are closer together indicate steep terrain; there is a lot of elevation change (as in our example, where each line indicates 20 feet elevation change) over a small lateral distance. Lines that are farther apart indicate flatter ground with less elevation change.
Concentric circles indicate peaks of hills or mountains; they are the highest elevation point and descend on all sides. Concentric circles with hatch marks inside – a number of short, perpendicular lines - show a depression.
You can see 2 depressions in this image, look for the short perpendicular hatch marks.
In valleys, the “V” shape formed always points uphill, with the stream channel passing through the point of the V. Streams are indicated on topographic maps with a blue line; if there isn’t a blue line, the V pattern will demonstrate which direction the water flows.
To teach this concept to children or others who are new to reading topographic maps, you can employ an easy exercise, called the Knuckle Map. The Knuckle Map demonstrates how topographic maps work .
Take a fine-tip marker in one hand, then ball the other hand into a fist.
Draw circles on each knuckle, starting at the very tip with a small circle and continuing out. Try to make each circle one millimeter lower than the previous one. After drawing on each knuckle, extending as low on the hand as desired, flatten your hand and look at it as if it were a topographic map.
Notice how the “steepest” part of your hand – the area immediately around your knuckle – has contour lines that are closest together. Notice the upward-pointing “V” shape in the valley between each finger. This demonstration is especially useful in helping kids and students understand the concept between topographic maps.
It should also be noted that Google Maps now comes with Topographic Google Maps. Now you can print them out for your area, and roam around to get a feel for how these maps translate to the physical world.
Reading Topographic Maps is an important skill to establish your position and to determine the location of landmarks or trails. The ability to interpret these maps is a key preparedness and outdoors skill.