The information below is an attempt at getting to the important particulars for teachers. This page is full of technical information and is designed to give teachers a way to decipher the manuals that come with most GPS units. You may only need bits and pieces of this information for your lessons. Position format conversions are a key piece in going from one application to another such as GPS to Google Earth. Please contact me with your interpretations and lesson plans at iteachgps@gmail.com. You can share with others at the companion blog to this site weteachgps.edublogs.org.

GPS 101

1. 1.How Does Global Positioning Work?
   

2. •Satellites
   

3. •NAVSTAR system is maintained by US Military
   

4. •Minimum constellation of 24 Satellites to operate; 28 to 30 satellites currently running in the constellation.
   

5. •Satellites transmit radio signals that terrestrial users pick up with GPS receivers
   

6. •2-D fix (position only) requires signal from 3 satellites; 3-D fix (position and elevation) requires signal from 4 satellites
   

7. •Other systems are under development in the world. Future units may have multi system capability, and GPS networks that charge for service have been discussed.
   

8. •GPS Receivers; Accuracy
   

9. •Civilian GPS units are used for automotive, marine, cycling, sailing, climbing, and dozens of handheld outdoor applications
   

10. •Professional applications range from surveying to delivery, aviation, geology and more all the time.
    

11. •GPS units process signals from satellites to provide location data
    

12. •Accuracy of most handheld units is 20 to 50 feet for position, 100 to 150 feet for elevation. Many times one can get a more accurate fix, but experience and feedback say to keep a large margin of error.
    

13. •Units that average positions are a little more accurate and the longer one of these sits still the closer it gets. Users can get a similar effect by taking several waypoints in one spot and positioning themselves at the center of the cluster.
    

14. •WAAS (Wide Area Augmentation System) is the free and most common form of correction for the GPS signal. By using a ground based reference point, WAAS and other differential corrections will provide more accurate positioning and elevation data. Most current handhelds will read the WAAS signal if you have line of sight with the WAAS satellites. With WAAS correction, position accuracy is usually less than 5m.
    

15. •The military and high-end municipal units use other differential corrections and a more accurate signal to get accuracy within a few feet or better.
    

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2. 2.Terminology
   

3. •GPS: Global Positioning System. Remember that this system, although funded and maintained by the US military, is global, and the NAVSTAR GPS constellation covers the entire globe. When there is no natural or human-made feature blocking the signal, terrestrial users should receive signals from 4-6 satellites at almost any point in the world. I have received as many as 10 satellites’ signals in Eugene, OR at one time.
   

4. •Waypoint: specific position. Position data can come in many forms in the US and around the world. Most handheld GPS units sold in the US default to the Lat/Long format of degrees, minutes, and decimals of minutes (DM). Many of the websites that use position data will also use this default format. Details on waypoint formats are included below under coordinate systems. May also be referred to as placemark or landmark.
   

5. •Route: a series of user created points linked together in a GPS unit. This has been a common question in the 101 classes. A route is created by the GPS user. A track is generated by the GPS itself.
   

6. •Trackback, Track Log: A track is the electronic breadcrumb trail that a GPS will leave automatically when the user sets this function. The track can be used to return to a location along the precise path followed (Trackback), or the track can be saved and named in the Track Log.
   

7. •GOTO: the button the user presses to go to a waypoint or begin navigation on a route or track.
   

8. •Trip Computer: data log. Defaults are usually speed, distance, trip distance, trip time, moving time, etc. GPS units can program as many as 40 different values for these data fields.
   

9. •Additional GPS Features (compass, altimeter, area calculator etc.)
   

10. •Electronic compass is very helpful in starting off toward a waypoint. The GPS unit will not necessarily be pointing in the start direction when a user is standing still. Many users will refer to a handheld compass for the first 50 feet or so. Once you have a satellite fix on your movement, direction will be more accurate. Units with electronic compass built-in will point in direction of travel when standing still.
    

11. •Barometric Altimeters are more accurate than GPS altimeter readings as long as they are calibrated properly. Altimeter in GPS provides visual elevation profile, ascent rate, descent rate and other data not available in a traditional GPS unit.
    

12. •Other fun and practical features available with some GPS units include area calculator, hunt and fish calendar, turn by turn driving directions, workout logs and heart rate monitors, Sun and Moon calendars and much more.
    

13. •Geocache: web-based GPS treasure hunting. Caches and geocaching enthusiasts now exist all over the world. Cache information includes a waypoint and a clue. The waypoint gets the user within 50 feet and the clue will help locate the cache. Caches range in size from tiny canisters to big Tupperware containers full of various things to trade. Geocaching enthusiasts sign the log in the cache and record their visits online.
    

14. •Virtual Geocache: a location that does not have a container, logbook to sign, or any trinkets to trade.
    

3. 3.GPS and Maps (Caution, this can get a little detailed)
   

4. •Coordinate Systems
   

5. •Coordinate systems around the world are based on placing a human generated grid over the map. Gerardus Mercator created the first grids that accurately represented the world as a sphere in 1569. Location data can be represented in dozens of different ways following different grids. The most common way of representing points on a navigational grid is the Latitude and Longitude system.
   

6. •Latitude and Longitude
   

7. •The following is a grossly over-simplified definition of latitude and longitude (One could generate enough curriculum from this topic alone to fill college classes). Latitude is related to the Earths polar axis. Longitude is calculated using time and the Earth’s rotation. So anyone who can learn the skill and apply it can determine their latitude and longitude. All other grids are arbitrary human creations placed on maps. The latitude number always appears first and represents the North/South position. Longitude always appears second and represents the East/West position
   

8. •There are three main formats, DM, DMS, DD, that are used to represent location data in the Latitude Longitude system. By understanding each of these formats and the punctuation used in recording the position, one can determine which format was used in a position.
   

9. •DM-Degrees and minutes. Most often the default format for GPS units sold in the US. Geocaching.com uses this format as the primary method of representing cache locations. Represented as a whole number of degrees followed by a “d” or the degree symbol. Numbers following this symbol end with an apostrophe to indicate minutes. Accurate positions in this format will have decimals of minutes in the number.
   

10. •DMS-Degrees minutes and seconds. This has been the customary navigation format for a long time and is commonly found on marine charts, USGS maps and much more. Represented by a whole number of degrees followed by a “d” or the degree symbol. Numbers following this symbol end with an apostrophe to indicate minutes. The next number is followed by quotation marks to indicate seconds. Seconds can have decimals for increased accuracy.
    

11. •DD-decimal degrees. This format is commonly used for surveying. DD is represented using a number with decimals followed by a “d” or degree sign.
    

Lat/Long formats and punctuation: (“d” can be a degree symbol)

1. •DM          ###d ##.##’        degree symbol, apostrophe   
   

2. •DMS        ###d ##’ ##.##”    degree symbol, apostrophe, quotes
   

3. •DD        ###.####d        degree symbol only
   

1. •Universal Transverse Mercator UTM
   

2. •NATO developed UTM in 1947 based on several countries’ grid map systems. Breaking the terrain into kilometer squares makes figuring distances on the map quick and intuitive. The MGRS (military grid reference system) is based on the UTM worldwide model. UTM is also the most intuitive way for most folks to get GPS waypoints off of a map. Lane County Search and Rescue, and the Willamette Pass Backcountry Ski Patrol are among the local organizations that use UTM for programming GPS and navigation.
   

3. •Other systems around the world
   

4. •Other grids and systems are mostly variations on the UTM system. Most current GPS units will accommodate dozens of grid and geodetic datum settings to match almost any map in the world.
   

5. •Atlas style grids are for map reference only and are not necessarily applicable
   

6. •Map Datum: Geodetic datum refers to the way the grid was placed on the map of terrain. The datum provides an anchor so that the grid remains accurate and consistent over large areas.
   

7. •WGS 84-World Geodetic System 1984 (revised 2004)
   

8. •Default datum for most GPS units and software applications
   

9. •NAD 27-North American Datum 1927
   

10. •Many older paper maps and all printed USGS maps
    

11. •Other datums
    

12. •Preparing your GPS for use with any map or coordinate system
    

13. •Remember DM format and WGS84 datum are the default for most GPS units and sites like geocaching.com. Often a GPS is ready to use for many applications.
    

14. •See above definitions to identify your position format and map datum.
    

15. •Different units may have a setup or preferences menu to get you to units or coordinate systems. Position formats and map datums have their own sub-menus as there are a lot of them. CONUS is a common abbreviation for continental U.S. With these steps, one can match the format and datum to almost any map in the world.
    

16. •On screen mapping and mapping software
    

17. •Different on-screen mapping software is available for compatible GPS units. formats include topography, street maps, marine navigation, fishing spots and much more.
    

4. 4.Waypoint Management
   

5. •Making a waypoint in the field
   

6. •Many GPS units have a “MARK” button on the control panel. Others are menu driven. Find “MARK” in the main menu.
   

7. •Waypoints can also be called landmarks or placemarks.
   

8. •Check the manual for the MOB (Man OverBoard) function. Designed as a way to make a quick waypoint when someone falls overboard, it also provides a quick way to enter waypoints anytime.
   

9. •Importance of names, icons, notes
   

10. •Always name your waypoints. You may remember what number 6 is for a short time, but later, or when it really counts, clearly marked waypoints make a huge difference. Many people devise a code to keep points organized. Geocaches usually start with GC, the rest can be up to you and fun. I use P for parking area, T for trailhead, C for camp and a few others. Students should have fun making up a class code.
    

11. •Keep your waypoints organized by archiving on your computer or deleting unknown waypoints. Computer software can also locate unknown waypoints and then you can name them.
    

12. •Icons are another way to organize waypoints and the field is usually next to the name field on the waypoint page. Some GPS units have the ability to search or organize by waypoint icon and many have a special menu for points with the geocache found or geocache unfound icons.
    

13. •Entering waypoints by hand (essential skill for geocaching)
    

14. •Make sure your position format and datum match.
    

15. •Start as though marking a waypoint (can be performed indoors with no gps signal as you will be using the point later)
    

16. •Highlight the position number and click enter.
    

17. •Each gps is either menu driven or you change a character at a time. These functions should all be similar to simple cell phone commands and computer menus. Many of the newer models have 4 and 5 way toggles that act like a computer mouse for navigating menus.
    

18. •Students often do well performing this task in a small group.
    

19. •Double check your accuracy. Lat/Long or UTM positions have a lot of digits. I had students crossing a footbridge on the river because they mis-entered data. They ended up across the river, several hundred meters from the actual position of the waypoint.
    

20. •Using waypoints, routes, tracking, how to GO TO
    

21. •Using the find function or menus for points, cities, routes, or tracks, select choice for navigating.
    

22. •Hit GOTO or start navigating.
    

23. •My favorite screen to navigate with looks like a compass with an arrow. Other options include a screen that look like a highway or navigating from the map screen directly.
    

24. •When to use GPS vs. when to leave in pocket
    

25. •Avoid having your attention on the GPS all the time. You are outside. Enjoy it.
    

26. •Walking on an established trail should only require occasional GPS checks.
    

27. •Attach GPS to high point on pack in order to keep tracking without holding GPS.
    

28. •When will GPS not work?
    

29. •Multi-path errors and terrain limitations. GPS units require line-of-sight with the satellites. Signals can bounce off of buildings or canyon walls and create errors. GPS does not work indoors or under bridges. Tree canopy may block signal.
    

30. •No power/dead batteries
    

31. •Military Shutoff: As the U.S. Military maintains the NAVSTAR system, the civilian signal may be shut off in times of military conflict.
    

32. •When brand new, some units need to be re-initialized. One of my students had a GPS making points about a mile from the actual position. The error corrected after he re-initialized the unit. Have the GPS find its position from scratch. Initializing can take 15 minutes. Once initialized, GPS units will usually lock on within a few minutes. Also re-initialize after the unit has traveled over 200 miles while it was turned off.