The cache is not at the posted coordinates. You will need to solve the puzzle in the listing to obtain the true coordinates of the cache. Fret not: the material in the cache listing is suitable for beginners, and designed to help you solve the puzzle.
Welcome to Pesky Coordinate Conversions!
This is an introductory puzzle cache that aims to give solvers an introduction to a selection of useful geographic coordinate formats and notations, for seamless use with the Global Positioning System (GPS). The knowledge gained here will be useful to aspiring cache owners thinking of planning and placing geocaches, as well as geocachers just getting their feet wet with the hundreds of Mystery and Multi-caches dotting the island. This is a companion cache to GC9HCDB (Rookie Mistake), which is of course also about coordinates.
Traditional Geocaching
In contemporary geocaching, Traditional brings to mind a generally simple process of getting oneself to the cache's location. Fire up the mobile app on a smartphone, select the green circle of your choice, hit 'Navigate', and you get an arrow pointing to the location and the distance you need to travel. You even get walking, public transport or driving directions on certain apps, bringing you to geocaches the same way your favourite mapping app brings you to school, work, the mall, your favourite nature park, or your friend's home. Do you know, or care about, the GPS coordinates of your office, or the mall? Yeah... probably not.
But smartphones with reasonably accurate location-tracking capabilities really only became a thing in the last decade; whereas geocaching was a thing for twice as long. To appreciate the significance of GPS coordinates in this context, one must first take a (brief) trip through geocaching history. How did geocachers in the early 2000s do it?
Garmin eTrex 10, a popular handheld GPSr
Many geocachers did, and some still do, use handheld devices called GPS receivers (GPSr). As the name suggests, a GPSr is a device that allows its user to obtain accurate information about their location using the GPS. This location information is presented to the user in the form of coordinates, which are usually used in conjunction with maps for one to obtain knowledge of their physical location in the world. To use a GPSr to get to a location, one has to obtain accurate GPS coordinates of their destination, and put them into the GPSr before they may obtain navigational assistance, which in its most basic form is a directional arrow with bearing and distance to the destination.
A GPSr is still the device of choice for people who regularly venture into areas with poor cellular connectivity, as all that is required to obtain location information from the GPS is an unobstructed view of the sky. But for urban and suburban geocaching, most of us will see a GPSr unnecessary as the smartphone has evolved into a powerful multifunctional device that integrates GPS information with highly accurate maps and intelligent navigation assistance. The use of a smartphone for geocaching has also all but eliminated the need for the modern cacher to deal with GPS coordinates at all - one can get by simply by navigating to pins on an electronic map.
That is, until the cacher decides to place a cache of their own, or ventures to special cache types, like Multi- or Mystery caches, which often present waypoints and final cache locations in the form of GPS coordinates.
Obtaining Coordinates
If you've placed a cache, you'll want to make sure the coordinates are accurate so that other cachers can get to the correct spot to search for your cache. It seems easy enough to fire up an app of choice on your smartphone, take a single reading, and use that one. However, this is an error-prone approach. The inaccuracies can be mitigated somewhat through GPS Averaging, an important technique that should be used in the field. Even then, if it's cloudy, or if you're indoors, surrounded by tall buildings or dense vegetation, readings are still bound to be rather inaccurate due to those obstructions.
Where it is difficult to obtain accurate GPS readings, how does one go about obtaining accurate coordinates? Using a map, of course! Though coordinates are concealed from view during most general use of popular mapping tools (since the average user won't need to bother about them anyway), they still are available fairly easily if you know where to look.
Let's head to Sentosa Gateway on Google Maps for a quick rundown.
Say we want the GPS coordinates of a point somewhere along the Sentosa Gateway footbridge. Locate the exact point, using the Satellite Layer if you require (click on the 'Layers' button on the bottom left). Now, left click on the exact point on the map. You'll notice some details popping up at the bottom of the map.
The numbers circled in red are the GPS coordinates of the point you just clicked on. Google Maps actually provides coordinates in another format, as well, and you can obtain them by clicking on the numbers circled in red.
Fantastic! We now know how to obtain GPS coordinates of any point using Google Maps! This is but one example - other mapping tools such as OpenStreetMap also provide ways to obtain coordinates of a point. In fact, cross-comparison of the coordinates of the same sat-view point obtained from different maps is yet another measure that can be taken to maximise accuracy.
But.. what do the coordinates mean? How do I read them.. and why do two sets of coordinates of the same point look different?
Geographic Coordinate Formats and Notation (for beginners)
Let's assume Earth is a sphere (it isn't exactly, but that's not too important for now). The North Pole is right at the top and the South Pole is right at the bottom. Imagine a series of vertical lines connecting the North and South Poles, specifying the east-west position on the globe - these are the meridians, or the lines that specify longitude. Then, imagine a series of horizontal lines, specifying the north-south position on the globe - these are the parallels, or the lines that specify latitude. The Prime Meridian separates the Eastern and Western hemispheres, while the Equator separates the Northern and Southern hemispheres.
Geographic coordinates therefore specify a position on the globe, based on the latitude and longitude of the position, expressed as angles and their various subdivisions. Commonly used coordinate formats are described below.
Decimal Degrees (DD)
+/- DD.dddddd
The DD format expresses latitude and longitude as decimal fractions of a degree, with positive degrees in the Northern and Eastern hemispheres, and negative degrees in the Southern and Western hemispheres. In DD notation, the latitudes are written first, before the longitudes. In our Sentosa Gateway example, the DD coordinates provided by Google Maps are: 1.261508, 103.823543 which tells us that the point on the map is located 1.261508 degrees North (of the Equator), and 103.823543 degrees East (of the Prime Meridian).
Degrees, Minutes, Seconds (DMS)
H DD° MM' SS.ss" or DD° MM' SS.ss" H
The DMS format expresses the finer divisions between each degree (°) of longitude and latitude divided into minutes (') and seconds (") of arc (see sexagesimal units). Google Maps also supplied DMS coordinates of our Sentosa Gateway example: 1°15'41.4"N, 103°49'24.8"E - this means that our point on the map is located at one degree, 15 arcminutes and 41.4 arcseconds North, and 103 degrees, 49 arcminutes and 24.8 arcseconds East. The same coordinates may also be written as: N01°15'41.4" E103°49'24.8".
One degree is divided into 60 arcminutes; one arcminute is divided into 60 arcseconds. Hence, one degree = 3600 arcseconds. Contrary to a common misconception, the "minutes" and "seconds" in sexagesimal coordinate notation have nothing to do with time.
Degrees Decimal Minutes (DDM)
H DD° MM.mmm
The DDM format is a rather unconventional one, but if you've been using the Geocaching.com website enough, you'll notice that cache coordinates are primarily presented in this format. The DDM format divides degrees (°) of longitude and latitude into decimal arcminutes. Take the posted coordinates of this cache for example: N 01° 18.045 E 103° 54.400 - this means that the blue "?" of this cache is located at one degree, 18.045 arcminutes North, and 103 degrees, 54.4 arcminutes East.
Coordinate Conversions
The use of several different coordinate formats and notations necessitates accurate conversion, in order for us to be able to solve geocaching puzzles, or just not get lost in the first place. Thankfully, we don't have to do them by hand. Many online tools exist to help us with accurate conversions, sparing us the horrors(?) of doing arithmetic by hand. A quick Google search gives us a buffet of options - see if you can find one that works well for you.
When you've found a suitable tool, try your hand at the following examples:
Drop me a message if you run into difficulties, and I will be happy to guide you along.
Other Coordinate Formats and Systems
The examples given in this listing are by far not an exhaustive list of coordinate formats in use in different GPS applications around the world. You may notice that in addition to DDM, Geocaching.com also uses UTM (Universal Transverse Mercator) coordinates, a coordinate system based on map projections. Certain puzzle caches may require solvers to convert to or from UTM coordinates. The intricacies of the differences between various coordinate systems are best left to a more advanced lesson, but you may open the can of worms anytime you wish with the abundance of information available online.
The Mystery Cache
Congratulations on making it this far! I hope that you have learnt a thing or two about coordinate formats, notation, and the importance of accurate coordinate conversions. Now it's time to be rewarded with a geocache find for your efforts. If you've paid close attention to the lesson, you will already have the information you need. Enter the final coordinates (in DDM format) into Geocheck, and if they are correct, you will be given a useful hint to the cache. Happy geocaching!
Further Learning for the Curious:
- How GPS Works Today (Youtube: BRIGHT SIDE)
- How Do GPS Coordinates Work? (Youtube: BrainStuff - HowStuffWorks)
- Coordinates Online Game (Mr. Nussbaum)
- Advanced: Geographic Coordinate and Map Projection (Youtube: GIS)
If you have any feedback, comments or suggestions for improvement of the information in this cache listing, please feel free to share them with me either in your logs, a message, or an email.