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For the past two decades, scientists have noticed a shocking change that makes things trickier for the US Department of Defense and trail hikers to find their way. While it is great to learn how to read the compass, the fact that the Magnetic North is also wandering around may mean that the dependable tool is no longer as dependable as it used to be.
Having a complete range of navigational skills, such as knowing how to read topographical maps will ensure that you will stay right on track regardless of what the terrain, weather, or the electromagnetic field of the earth might be up to.
The Beginning of Topographical Maps
Before you delve into the more technical knowledge of how to read topographic maps, here is a bit of a backstory. A man named John Wesley Powell invented topographic maps.
Powell was a geologist and Union army veteran who convinced Congress in 1884 to authorize a meticulous cartography project wherein his team would systematically develop topographic maps to have a better understanding of the hydrology and resource potential of the western landscape.
This was a tall order, with surveyors required to manually conduct most of the measurement work with the use of aneroid barometers for calculating altitude and compass traverses and steel tape measures for spatial distances.
The land’s contours according to the measurements that the surveyors collected were etched into large copper sheets that could be used later for printing and reprinting the very first topographic maps. All the heavy equipment had to be transported by mule to the backcountry.
The topographic map project of Powell was an ambitious and huge undertaking. However, the payoff was not just to help the federal government plan the right way of using resources, or for the geologists looking for minerals. This was also to help outdoor enthusiasts have safer and more confident navigation knowing that they were armed with the skill and knowledge of reading a topographical map.
Understanding the Scale on Topographic Maps
It is very easy to read a topographic map the moment you become familiar with the details. The first thing to do is look for the scale of the map that will inform you of the amount of detail contained in the map. The scale on topographical maps will let you know how many fractions of a mile or miles are represented by one inch. When the scale is smaller, the map will also have more details.
If the scale is larger, the paper will also represent less detail. For instance, a topographic map of the entire United States might be several feet in width and length but doesn’t contain almost all the navigable information that you might find in a pocket-sized map of North Carolina’s Grandfather Mountain.
Once you become familiar with the scale that your map represents, you can begin taking in other details. The legend of a topographic map, just like other kinds of maps, will inform you of what different types of lines, colors, and symbols represent from waterfalls to roads, rivers, and more. The legend also includes other data you will need for correctly reading a topographical map and using this for navigation.
How to Read the Contour Lines on Topographic Maps
Make sure you pay attention to the contour and magnetic declination and index-line intervals. These details are crucial for reading the map properly.
The contours on the topographic map will tell where elevation changes will occur on the landscape, while the contour interval will tell you how big a shift is represented between the map’s contour lines.
For instance, a map with a contour index of 20 feet is going to show changes in elevation in increments of 20 feet.
A topographic map will not only indicate where elevation changes happen in the landscape but this will also let you know how graduate or steep these changes are going to be. If the map with a 20-foot contour index shows a landmass with a series of 10 concentric lines that are tightly spaced, you can expect a 200-foot elevation gain to take place faster than 10 contour lines of similar scale that is drawn over the map’s broad area.
Taking note of the spacing of the contour lines can also help determine the location of peaks, cliffs, saddles, ridgelines, ravines, and gorges, and what it may be like to try to navigate that specific terrain. This is a great way of estimating if certain backpacking or hike route is safely within your personal technical skills.
Aside from the main contour lines that are often bolder compared to the rest on the map and are known as index lines, the map may also have supplementary contour lines that show smaller elevation gain increments for additional detail.
This, combined with legend’s features such as streams, creeks, and rivers can help you not where moving water has carved valleys over centuries or where you can find dry washes that might be risky in flash floods.
Using Magnetic Declination on Topographic Maps
Another feature that makes topographical maps very handy and helpful for hikers is none other than magnetic declination. It is how you could adjust for the variances between magnetic north and true north that may make you veer off course.
Regardless of how far the separation is between the magnetic north and true north, searching for the magnetic declination, or the angle between the true north and magnetic north, can be found with the use of the topographic map’s legend and with the help of other tools.
Reference the map first to adjust for declination. For instance, if you are east of the Mississippi River, you can have the declination adjusted in the westward direction. When you are west of the river, the declination angle should be adjusted in the eastward direction. You can think of the river as zero while the declination on both sides is negative or positive.
Turn the middle of the compass based on the declination angle on the legend of the map to adjust the compass to follow to the grid north where the map is based instead of magnetic north. This keeps you well-oriented and on trial and is a major aspect of reading topographical maps.