Don’t Get Lost
2/1/2002

Team CacheCows

I heard a story recently about an emergency call the National Park Service received from a cell phone that a group of hikers had with them. It seems that they were lost and needed rescuing. When the NPS headquarters asked them if they could provide some kind of a landmark they could use to locate them, the hikers provided their exact latitude and longitude! When asked how they could be so precise, they replied that they had a GPSR with them, but hadn’t brought a map nor had they marked their starting or destination points! The goal of this article is to help you not repeat their plight…

I’d like to tell you where to go: You probably remember your basic map skills from grade school; remember all that latitude and longitude stuff? Remember how it had to do with time and temperature? Perhaps not, but it sure had something to do with degrees and minutes and seconds! If you want to describe a location on the Earth, the most common manner is to use the imaginary horizontal and vertical lines drawn around the globe known as latitude and longitude. The latitude lines are the horizontal ones that parallel the equator, and longitude are the vertical ones. Latitude lines are measured from the equator, known as 0°, to either 90° North at the North Pole, or to 90° South at the South Pole. Longitude lines are measured from the 0° line that starts at the North Pole, through Greenwich England, and ends at the South Pole. Longitude lines West of this 0° line are numbered up to 180° West, and lines East of the 0° are numbered up to 180° East. If you think about it, 180° West is the very same line as 180° East; its the line on the exact opposite side of the Earth from the 0° line. Note that it is very common to see longitude lines East of 0° to simply be numbered 1° through 180°, and for lines West of 0° to simply be numbered -1° through -180°. Since the Earth is 25,000 miles in circumference, dividing it into only 360° of longitude and 180° of latitude leaves a pretty big area. Roughly 4,761 square miles per intersection! To define a location with more precision, each degree of latitude and/or longitude is broken down. Each degree is broken down into 60 subdivisions known as minutes and each of these are further broken down into 60 sub-sub-divisions known as seconds. For example, the Washington Monument is located at 38° 53′ 20" North by 77° 2′ 6" West. Notice how minutes are symbolized by the (‘) character and seconds by the (") character?

Variations on a theme: While Deg/Min/Sec is the best known means of describing a location in latitude and longitude, its not the only way. In this section, please keep reminding yourself that minutes are nothing more than subdivisions of degrees, and seconds are nothing more than subdivisions of minutes. In a salute to the metric system, there are two other very popular ways of expressing latitude and longitude. The first does away with seconds by replacing them with either two or three decimal places of minutes. This first format is expressed simply as Deg/Min.mm (2 decimal places) or as Deg/Min.mmm (3 decimal places). To convert from Deg/Min/Sec simply divide the number of seconds by 60. So the Washington Monument would be located at 38° 53.333′ North by 77° 2.100′ West (20 seconds / 60 = .333 and 6 seconds / 60 = .100). The second format goes even further, and eliminates both minutes and seconds and is known as decimal degrees. To convert Deg/Min/Sec to decimal degrees, you have to first convert to Deg/Min.mmm and then divide the resulting Min.mmm also by 60. So the Washington Monument would be located at 38.88888° North by 77.03500° West. In Geocaching, Deg/Min.mmm is the most used format. There are a couple of tools we will discuss later; Mapblast uses decimal degrees and Topozone can use either decimal degrees or Deg/Min/Sec. Get used to using negative numbers for longitude West of 0° rather than using West, almost all tools work this way. Every location in North America is expressed as a negative longitude.

So now I know where to go, right? Well, not quite… If I were to tell you I was at N38.88888 -77.03500 you would know I was at the Washington Monument, right? No, its not that easy… While latitude and longitude have certainly been standardized, how each spot on the Earth is assigned its latitude and longitude has not. There are over 70 systems in use that define the precise latitude and longitude for everywhere on Earth, and they don’t match up with each other. The main reason for this in a nutshell is that when measurements were made over the years, methods, mathematics, and tools got precise, and errors were reduced. These 70+ systems are known as Datums. So, if I really want to tell you about a location, such as where the Washington Monument is, I not only have to tell you its latitude and longitude, but I also have to tell you what datum I’m using. Time for a side note: your GPSR actually only uses one datum internally. Almost all GPSRs have the ability to talk to you in many many datums, but all it is actually doing is converting from its internal datum to the one you want to use, and displaying it that way. There are only three datums we need to worry about in Geocaching; NAD27, WGS84, and NAD83. NAD27 (North American Datum of 1927) is the datum used on USGS (United States Geological Survey) topographical maps. When you use the tool Topozone, every coordinate you enter or take from their maps is NAD27 datum; your GPSR must be set for NAD27 if entering or reading coordinates for use with a topological map. WGS84 (World Geological Survey of 1984) is the datum used inherently by the Global Positioning System, and is what is used on www.geocaching.com. You must have your GPSR set for WGS84 datum when entering waypoints from geocaching.com, and can usually just leave it set this way. NAD83 (North American Datum of 1983) is the datum used by the Mapblast and Terraserver. For all practical purposes in Geocaching, you can consider NAD83 and WGS84 to be identical when describing a point in North America. By the way, the difference between a location described in NAD27 and WGS84/NAD83 using the same latitude/longitude can be up to 328 feet off in each direction!

Entering a cache into your GPSR: First, make sure that your GPSR is set to use latitude and longitude expressed as Deg/Min.mmm, and also make sure its set to use WGS84 datum. If your GPSR is not set up this way, you will not find the cache you are hunting. Now, enter a new waypoint into your GPSR using the latitude and longitude displayed on the cache’s page. For example, to hunt CacheCows Tales From The Crypt, you would enter a latitude of 42 ° 38.000′ N and a longitude of 88° 46.369′ West. If the cache’s page suggests a parking location and/or trailhead, enter those points as additional waypoints. Use waypoint names and descriptions that will help you remember what they are for.

Tools to help figure out where you are going: On the cache’s page at geocaching.com, towards the bottom, you will see three links to generate maps: Driving directions from Mapblast, topographical maps from Topozone, and satellite photos from Terraserver. Use the driving directions link to figure out how to get as close as you can to the cache, but remember that these driving directions are to the cache location, and not to the parking/trailhead location if one was given. Try and figure out a good starting place to drive to from these maps. Next use the Topozone link to view a topographical map of the cache’s area. Use this map to try and determine a good way to attack the cache. NOTE: at this time, geocaching.com does not convert the cache’s coordinates from WGS84 to NAD27 when going to the Topozone map; therefore the displayed map could be wrong by up to 328 feet in each direction. Also take a look at a great tool called ExpertGPS from Topografix. From each cache detail page at geocaching.com you can download the cache’s waypoint directly to this $60 program, and once downloaded you can view the exact spot on a topographic map (it converts to NAD27 for you), or display it on a satellite photo, and you can upload it to your GPSR.

My favorite use though is when I get back from a cache. While hunting for a cache I turn on my GPSR’s tracking function, then when I get back I download my track directly to ExpertGPS and print out my trail on both a topo map and satellite photo to see exactly where I walked! You can get a 14 day trial version of ExpertGPS from the website. NOTE: ExpertGPS has no built in maps or photos, it downloads them in realtime from the Internet. If you do not have an Internet connection when using ExpertGPS, then maps and photos will not be available to you. ExpertGPS also does not have a moving map feature, that is not its purpose in life; but its perfect for Geocaching!

Hit the road, Jack: Now its time to head to your starting point. Once you park your car, it is time to do a VERY important step: mark your current position as a waypoint. This way you will be able to get back out of the woods to your car! Now set your GPSR to GoTo the waypoint you entered for the cache, and let it lead you to it. Stick to the trails until you get as close to the cache as possible. Sometimes it may seem that the cache is getting further away, so check and see if the trail curves around closer to the cache, or see if there are other trails to try.

Zeroing in: If during the hunt you find that no matter what trails you take you can’t get any closer to the cache, it is time to leave the trail. NOTE: the vast majority of caches are within 300 feet of a trail. Before you leave the trail, there are three important steps to take. When your GPSR says you can’t get any closer to the cache from the trail, or anytime the GPSR says you are less than 150 feet from the cache, STOP moving. Give your GPSR at least two minutes to settle down. NOTE: If you purchased a GPSR with built-in averaging as we suggested on our What do I need? page, then this step will help A LOT! Once your GPSR has settled down, mark your current location as a new waypoint. This will allow you to get back to the trail again. The third step is to get out your compass and see in which direction the cache lies according to the bearing your GPSR is giving. READ HERE why a compass is so important. Now its time to pace off the distance remaining to the cache according to your GPSR. Remember that the GPSR is only accurate within 50 to 100 feet of the cache. If your GPSR says you are within that distance, start looking on your own. Look for places that you would hide a cache. Look up and down. Look under logs and rocks. If you are really stuck, grab the cache page you printed out and try the coded clue! Good luck and have fun!