Frequently Asked Questions
Q: What is GPS?
A: GPS is an acronym for Global Positioning System. It is a satellite based navigation system that was created by the US military but anyone around the world can use it. It is ideal for ships, planes, cars, and hikers. The cost of a handheld GPS receiver starts at about $100. A GPS receiver will tell anyone where they are within about 100 feet, anywhere on the planet.
You should take the time to practice with a GPS receiver before you try to understand the technical details of the GPS system. They are surprisingly simple to use, given all the technology involved. You can learn most of what you need to know within and hour or two of opening the box. They usually come with a tutorial, use it! It only takes about 30 minutes to follow this tutorial and you will learn a great deal in a short period of time.
Unfortunately, most tutorials do not explain how to use the GPS unit with a topographical map. Visit the Garmin website for detailed information on the GPS system.
Related FAQs: “How do I use GPS to find my way?” and “What is UTM?”Q: Is a GPS the only navigation tool I need?
A: A GPS unit is only a tool that will compliment your navigation skills and other tools!
If you are lost in the wilderness and you pull a new GPS out of the box, insert batteries and read the manual, you will still be lost. (RMRU has rescued people in this exact situation.) A GPS unit is not a replacement for a map and compass.
At a minimum, you will have needed to prepare by doing one of the following:
Bring a map and compass and know how to use them (the compass is optional if the GPS has a digital compass built in).
Turned the GPS on and let it track your route as you hiked so you can follow you path back.
Entered way points for known locations like trail heads, camps, ranger stations, etc..
Doing any of the above (preferably all) will be the only thing that helps you when it is time to use the GPS.Q: How do I use GPS to find my way?
A: Click here for downloadable pdf instructions Q: How do I use a map, compass, and altimeter?
A: Some instructions never seems to make sense until you actually try to do them. This FAQ is one of those things. Simply reading without trying the exercise may be confusing. Click here for downloadable pdf instructions
A map, compass, and altimeter can be used for two general uses. One, to find where you are and two, to determine where to go. Take the time to practice before you need to use these skills. Practice often.
To find where you are:
Triangulation Method: First, find two landmarks. It helps if they are close to 90° from each other relative to your position. Next, take a bearing for these landmarks. Add or subtract the magnetic declination. Plot these bearings on your map. The point where the two bearings intersect is your position. The same can be done with several landmarks for more accuracy.
Altimeter Method: This method works best if you are on a trail, ridgeline, or valley that contains a large section that is all uphill or all downhill. It can also be used in conjunction with the triangulation method to determine your position more accurately. First, be sure that you altimeter has been calibrated. Next, find the point on your map where the trail, ridgeline, or valley intersects the contour line that most closely corresponds to your altimeter reading.
To determine where to go:
If you are on a trail but you can not determine if you are going in the right direction, a quick glance at the map and compass should sort things out.
If you are not on a trail, you will need a more precise method of determining the correct direction of travel. First, plot your desired course on your map to determine your true compass heading. Then add or subtract the magnetic declination. Now hold the compass at eye level and take a bearing to determine which object on the horizon you want to head for. Start walking toward that object until you reach it or loose site of it. Repeat the process until you reach your final destination.
Terms and methods: Click here for downloadable pdf instructions
Q: What is UTM?
A: UTM is an acronym for Universal Transverse Mercator Grid System, but please don’t try to memorize this because it’s not very useful (except to impress your simple minded friends). UTM is the most common of many grid systems. It is used to provide position information much the same at latitude/longitute (LAT/LON). The reason grid systems were created was to simplify the process of calculating and plotting positions and distances.
If you have ever tried to calculate your LAT/LON on a map, you probably found that it is not an easy task because the size of each degree, minute, and second changes relative to your latitude. UTM uses a constant of 1 unit = 1 meter regardless of your latitude.
Note: There are many web sites that explain everything you would possibly want to know about the UTM system, especially on how the each grid is constructed. You do not need to know this to use UTM.Related FAQs: How do I use UTM?
When should I use UTM instead of LAT/LON? Q: How do I use UTM?
A: Click here for downloadable pdf instructions Q: What is an Interpolator?
A: Each UTM grid on a 7.5 minute USGS map is 1000 meters square. An Interpolater is an overlay which is used to break each grid down into 100 meter squares. Now that you have 100 meters squares, you can further increase you precision by estimating 10 meter increments in each square. View and print the Interpolater in PDF format (provided by Steve Bryant). Print it on a transparency then laminate it for strength. This Interpolater should be used with a 7.5 minute (1:24000) map.
Click here for downloadable pdf instructions
Q: When should I use UTM instead of LAT/LON?
A: That depends on who you are communicating with. Usually hikers use UTM while pilots and sailors use LAT/LON. Pilots and sailors have been using LAT/LON long before UTM was invented. LAT/LON is well suited for long distances (miles). UTM is better suited for short distances (meters). Q: How do I manually convert UTM to LAT/LON
A: You don’t. Let your computer or GPS unit do the conversion for you. The formula is extremely complex and considered nearly impossible to do manually.