In the first part of this article, we covered how to read a topographic map. Take a look at the article and re-familiarize yourself with the concepts, as we will assume knowledge of contour lines, topographic maps, and the different colors used on the map for this article.
Latitude and Longitude
Most guidebooks generally will list GPS trailhead coordinates as directions to find the trail. Perhaps you've seen something akin to the followng:
- Latitude N 40 26' 16.7"
- Longitude W 75 4' 35.9"
But, what does this information mean? And, how will you interpret it with a map?
Latitude lines run from east to west around the earth, while longitude lines run north to south. Looking at the example above, you can see that both latitude and longitude are each measured using three variables: degrees (°), minutes ('), and seconds ("). When interpreting latitude, it is easiest to remember that the equator is 0° latitude. It divides the globe into the Northern and Southern Hemispheres, which is why latitude is first described in a manner specifying if it is in the Northern or Southern Hemisphere.
Likewise, longitude is described firstly by whether it is east or west of the prime meridian. Prime meridian runs through Greenwich, England, and is used much like the equator for bearings. Longitude runs from 0° to 180° both east and west of the prime meridian. When looking at the map, the x-axis (horizontal lines indicating latitude) and the y-axis (veritcal lines indicating longitude) are each divided into degrees. Using the example above, start with the latitude which is in the northern hemisphere at 40°. Find that on the map. Now, find the longitude which is west of the prime meridian at 75°. Where the two lines intersect is in Pennsylvania.
It is by adding the minutes and seconds into the description of your latitude and longitude that you are able to accurately pinpoint an exact place on the map. (For our Pennsylvania readers, the coordinates above refer to the trailhead of Tohickon Creek).
Map Scale
When purchasing your map, it is important to note the scale of the map. The scale is denoted as a ratio of map distance to ground distance. Map scales are typically 1:x (with x being the ground distance). The units used to describe the map distance will be consistant with the ground distance, and are usually defined in inches, feet or meters. Another good rule of thumb is that the smaller x is the more detailed the map will be, while the larger x is the less detailed the map will be. Typically, you will find that maps are 1:24,000 (in which 1 inch of map equals 24,000 inches - or 2,000 feet - of ground, and happens to be the primary scale used by the USGS for mapping topography in the U.S.) and 1:63,360 (in which 1 inch of map equals 1 mile of ground).
Generally, you will want to purchase a 1:24,000 map unless you are planning a long-distance backpacking trip, in which case a smaller scale map (i.e. 1:250,000) may be the way to go.
Compass
We purchased our first compass after taking a fundamentals class on using a map and compass (something that we highly recommend to all beginner hikers - you should be able to find a local class wherever you may live). Up until taking that class, we would have probably purchased the wrong type of compass for our needs. As with anything, there are many varieties, and it's best to know what kind you'll need while on the trail.
Take a look at the picture of the compass on the left. This is a magnetic compass that orients based upon the magnetic field of the earth. You can see that the compass is on a plastic base plate that has a straight edge and ruler, as well as a magnifying bubble. The orienting arrow is the fixed lined red arrow pointing directly at North, while you can see that the magnetic needle is pointing to approximately 340°. The direction of travel arrow is the fixed arrow which you can see right above the magnifying bubble.
When purchasing your compass, you want to make sure that it is a magnetic compass with adjustable declination. What is declination? Declination is the angular difference between the True North and Magnetic North. True North essentially refers to the north pole, while magnetic north refers to the direction the north end of the magnetic needle points.
How do you use a map and compass together? How would you use these items to get your bearings? And, why exactly would you want a mirror with your compass? These are concepts outside of the scope of The Ten Essentials articles, but will be covered soon enough
We hope that our readers now have some basic information to help them in not only understanding the importance of this first essential, but also what they should be looking for when they are going to purchase their first (or second or third) map and compass.
If any of our readers have any other suggestions, please post in the comments section below.