While they may look intimidating, all hikers should learn how to read a topographic map. Why? Well, even though physical maps show the landmarks of an area, they’re not very good at showing elevation. Instead of using a specific system for showing the height, specific colors on an ordinary map stand for ranges of elevation (e.g. green can indicate 0-2500 feet). When you’re relying on a map for your safety, wouldn’t you prefer something a bit more precise? That’s where a topographic map comes in handy.
What is a topographic map, and what is it used for?
Topographic maps are two-dimensional representations of a three-dimensional landscape. They show the basic landmarks of the area:
- Man-made objects like roads, buildings, railroad tracks, and airports
- Sources of water such as lakes, streams, rivers, and swamps
- Areas of vegetation (or lack thereof) like vineyards, orchards, forests, and open areas — places that are almost always snow-covered, or open fields
- Other natural features such as mountains, valleys, and cliffs
The most useful feature of topographic maps is the precise way that they portray the shape of the land. These maps are designed to show where the terrain will rise and fall and how quickly it will do so. This can help you decide how to tackle a mountain or a valley — or if you want to! This means that topographic maps are handy tools for hikers, but they’re also used by government agencies to help with urban planning and development, mining, and in emergencies or rescue missions.
Parts of a topographic map
In order to understand how a topographic map works, you have to be familiar with its parts. The most important part is the legend, which shows:
- The name of the map.
- The year of production, or when the map was originally made.
- The year of revision, or when it was last updated.
- The general location within the area, shown as a dot or a rectangle within the outline of a state, province, territory, etc.
- The next adjacent quadrangle map. This is the name of the map that connects to the one you’re using, and where it is in relation, e.g., to the northeast.
- The scale, which shows the proportion between distance on the map (in inches or centimeters) and distance on the ground. There are three types of scales:
- A verbal scale is the simplest of the three. It relates inches or centimeters on the map to feet, meters, miles, or kilometers on the ground, e.g., 1 inch = 2000 feet.
- A fractional scale is expressed either as a ratio (1:62500) or a fraction (1/62500). There may or may not be units attached. If there aren’t, you get to choose your own, e.g., 1 map inch = 62,500 ground inches, 1 map centimeter = 62,500 ground centimeters, and so on. You’d then convert your chosen unit to feet, meters, miles, or kilometers.
- A bar scale is a line drawn on the map that represents both map units and ground units. It will often be broken into smaller numbered pieces. For example, if the entire bar represents 5 miles, it will run from 0 to 5. To keep from getting confused by the numbers, count the number of boxes in the scale. A 5-mile scale will have five boxes. One advantage to a bar scale is that if you want to enlarge or shrink your map, it will still be valid, whereas verbal and fractional scales will not. Keep this in mind when choosing your map.
- The contour interval (we’ll get to that soon!)
- The magnetic declination, or the difference between true north (the location of the North Pole) and magnetic north (the direction your compass needle will point). Declination varies depending on your location and if you don’t account for it, you could end up in a completely different location from where you aim to go. The symbol on your map shows what the declination is for where you’ll be hiking so you can adjust your compass accordingly for an accurate reading and bearing.
- The latitude and longitude.
There are also colors and symbols to take into account when reading a topographic map. These will be listed in the map’s key or legend, but familiarizing yourself with them will save you time.
- The colors on a topographic map are used to distinguish between types of landmarks. For example:
- Red is for roads and, within the U.S., surveying features that belong to the U.S. Public Land Survey.
- Black is for man-made objects.
- Blue is for water.
- Green is for vegetation.
- White is for areas where there is sparse vegetation or none at all. This could include desert, grass, sand, rocks, snow, boulders, etc.
- Purple is for features that have been added to the map due to aerial photographs, but have not been checked in the field.
- Boundaries aren’t physical features, but are important to recognize as they show when you cross into a national forest, or a different city, county, or state. They’re marked with broken lines of different dots and dashes for specific types of boundary.
- Benchmarks show where the elevation has actually been surveyed. These are marked with a triangle if a marker was placed in the ground at that location, or an X if no marker was left behind.
One of the most important features of a topographic map are the contour lines, which are shown in brown.
How do contour lines work?
Contour lines are drawn around areas that have the same elevation, and the space between them represents a change in elevation. They’re also drawn to reflect the shape of the land. Basically, they give you a picture of what the terrain looks like and show where the ground gets higher or lower. Follow the contour lines and elevation indicators to determine the change in elevation. The closer together the contour lines are on a map, the steeper the rise or fall will be. You should also bear in mind that contour lines won’t indicate every bump in your road. If a sudden change in elevation occurs between them, it won’t be indicated.
How do you determine contour intervals?
Even though contour lines can be close together or far apart on the map, the space between them represents the same change in elevation. That change in elevation is called the “contour interval,” and it’s the same for the entire map. It will be listed in the margin of your map for reference, as the contour lines usually won’t be labeled themselves. Sometimes, however, there will be index lines to help you out. Since there can be many contour lines on a single map, every fifth line (the index line) will be labeled with an elevation. To help you spot them easily, they’ll be thicker than regular contour lines.
How to read a topographic map
You next want to put your knowledge of contour lines and intervals together to figure out what they mean. For instance:
- The closer together the contour lines, the steeper the slope.
- The further apart the contour lines, the gentler the slope.
- If you see contour lines that form a V pointing uphill, you’re looking at a valley. This will usually also indicate a stream or a river that runs downhill from a higher altitude.
- If you see contour lines that form a V pointing downhill, you’re looking at a ridge.
- If you see a contour line in a circle with no other lines inside it, you’re looking at a summit.
- If you see contour lines in concentric circles and they’re marked by hachures, you’re looking at a depression, or sunken geological formation.
This helps you plot your best course across the landscape — if you want to take it easy, you can avoid difficult climbs, whereas if you want a challenge, you can head toward more rugged areas. By noting the many landmarks these maps list, you can ensure you don’t hike into unsafe areas like mineshafts or caves, and you can determine where to make camp by knowing where forested areas with water sources are. You can also determine what supplies you’ll need by analyzing the area. As you can see, topographic maps are incredible resources. Any hiker should have one on their list of essentials and know how to interpret their information. Hopefully after reading this guide, you feel confident and ready to take on your next adventure. Related: Hiking Tips For Beginners