Topographic Maps – Understanding The Features
Topo Maps Are Great, Having The Correct Topo Maps Is Better
Topographic maps are a must have when backpacking, even when you use a GPS device. If GPS fails or you are out longer than planned, accept no substitutes for physical topo maps. Having a topographic map is an asset but having the correct map makes a huge difference. Knowing how to read and what to look for is vital and dependent on your purpose. Comprehension of the features, how to read, when it was last updated and what the scale is are important things to know. In addition, understanding what true north, grid north and magnetic north are is key to proper navigation as they are not equal.
Topographic Map Features
Features of the topographic map you use will differ depending on your specific use and purpose. For backcountry trekking, a smaller scale is more desirable than general hiking on an established trail with markers. Color is great if you want to see more detail in features and elevation. Land use and land cover maps are very useful to hunters or fishermen. Contour lines will show you levels of elevation and how they change over distance. Latitude and longitude lines are used in defining specific points and gathering bearings or directional indicators. Maps for our purposes here will surround backpacking and more precise navigation.
Scales For Backcountry Use
With backpacking and bushwhacking through the backcountry in mind, we want to use 7.5 minute series maps. Otherwise known as 1:24,000 scale maps. These maps provide more detail on land as well as elevation and are therefore ideal for ground navigation. On these maps, 1 inch represents 2,000 feet. ~2.5 inches is about a mile. Keep in mind that while these are favorable for precise navigation, they only cover about 55 square miles. Pack many if you plan on traveling vast distances!
Contour Lines
Knowing how to read contour lines is one of the most useful skills to acquire when using topographic maps. The contour lines provided detail of elevation over distance and create a detailed picture of the land using the flat map. There are a few things to know about contour lines:
- Contour lines are indicative of elevation above sea level.
- Contour lines are points of equal elevation connected.
- The contour interval is the difference in elevation between counter lines. Not every map uses the same contour interval!
- Lower contour interval translates to higher detail.
- Land features are visible with contour lines. V-shaped contour lines close together indicate a sharp drop in elevation. This feature may be a canyon or maybe waterfalls if there is a river or stream. The v-shape always points upstream on any waterway shown on the map. U-shaped contour lines mean there is a hill or ridge feature.
Latitude & Longitude Lines
Lines of latitude are on maps which run west-east and are parallel to the equator. The equator is the starting point, thus it is 0 degrees. Lines of longitude are the opposite of latitude, they go from north-south. Starting point for measuring longitudinal lines begin at the prime meridian. The international prime meridian is located in Greenwich, England and is the 0 degree point.
For general use, degrees will work but are not the most precise coordinates. Degrees are divided by minutes and seconds to increase location accuracy. Minutes are represented with ‘ and seconds with “. An example of an approximate location would be 39° 6′ 11.2284” N, 84° 30’ 43.2576” W. The coordinates can also be stated as decimal readings for degrees: 39.1031° N, 84.5120° W.
The Three Norths
Knowing the difference between the three norths is also important, this applies to use with any map and/or compass. Generally speaking, north means up right? Well, kind of. Geographical north is the north which the lines of longitude run alongside. This is the north on a map which is a flat surface.
The vertical grid lines printed on topographic maps represent grid north. These lines are not 100% straight and are a representation of the curvature of the planet to minimize directional error. To compensate the curvature of Earth with the readings on the flat map we use declination.
Magnetic north is the direction the compass indicates as north. The reading derived by compass is from the magnetic North Pole. A problem with the reading of north toward the North Pole is that it is not truly located at 0° N, 0°W. Magnetic north is a few hundred miles away and moving. Right now it is somewhere on Ellesmere Island, Canada.
Navigate by grid north when using topographic maps. Using grid north to navigate is fine in the backcountry.
Source The Right Maps
Taking into account your purpose and use, find the correct maps. Having maps with the wrong features, large scales and outdated information can make navigation tougher than it needs to be. Understanding how to use topographic maps and read them is non negotiable.
