A short guide to a better understanding of GPS coordinates and their different formats
Global Positioning System (GPS) are getting more popular nowadays that even mobile phones are capable of GPS navigation. Even photo cameras are now able to receive GPS coordinates and add the location to the photo meta data. In the outdoors, GPS is a great additional tool to your old-fashioned paper maps. If a GPS is used properly, it is certainly the most accurate and safest way to navigate, but you should not solely rely on your GPS. Out there, you usually use raw coordinates rather than saved streets or other points of reference (note that there are no topographic maps of the region available to load on your GPS). Here in the region, where addresses are commonly described by landmarks rather than street names, city navigation can get challenging even with a handheld or built-in GPS in your car. With the ever-changing infrastructure, maps are already outdated before you can even load them on your GPS. But if you work with raw coordinates, they will last forever.
GPS is able to give you the exact* location or destination you want to reach, but this does not mean it also provides you the optimal way to get there. Especially if you use the GPS outdoors and not based on a saved road system, the GPS will always give you the direct and straight way to the next waypoint no matter if there are mountains, cliffs, wadis or any other obstacles in your way. So good route planning and ideally a map are still essential when going outdoors. Unfortunately as mentioned earlier, there are no paper maps for the mountains or desert available, so you need to rely on visual planning on-site or advanced planning using a satellite map, which might be very inaccurate. Currently, your very best source of information is, if you can get, the whole route files plotted with the track and the waypoints from someone who made the trip before. If you go on a hike, the GPS will plot your route even if you don’t save waypoints, this route can be exported and shared with others. (The advanced guide book “Off-Road Adventure Routes, UAE and Oman” written by Mike Nott is based on GPS route files). Even if you attempt a route for the first time, this tracking can be a lifesaver since you will be able to retrace your exact* way back. At the mountains of the region, this can be essential, since a few metres can make a difference between life and death.
*Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Official accuracy is 3m to 15m for public use, but usually the accuracy is much better than 3m.
Let’s get back to the technical side. To use raw coordinates, you type in a set of numbers rather than street names or landmarks. You should have some little knowledge about the coordinate system and how it works since there is no uniform standard for providing GPS coordinates.
How it works:
GPS is based on the mathematical theory of triangulation. The GPS, no matter if in a phone, handheld or built-in, acts as receiver at an unknown location. To calculate the location (theoretically), three known points in space are required. Satellites, which are circling on fixed orbits, send their exact positions to the GPS receiver. The GPS then calculates based on the distance and locations of each satellite (practically, a GPS needs at least five known spots or satellites to work accurately) its own location. That’s the very basic explanation, and there is a bit more behind it, but that will do for now to get a better understanding of the system. Therefore, GPS systems only work under open sky. In a deep and narrow valley, you might not be able to catch the signal of enough satellites and the GPS might not work. But the signals are still strong enough to go through the windscreen of a car and it’s possible to use even handhelds in the car without external antenna.
GPS is an electrical device which needs batteries and can also get broken especially in the outdoors. Therefore, you should be familiar with your surroundings and ideally have an alternative map and compass as backup with you (and also need to know how to use them).
Types of coordinates systems:
Latitude and longitude
The most common coordinate format and also the format we use in the magazine are based on latitude and longitude (in degrees and decimal minutes). Since we are not in aviation, the elevation is not so essential as we are bound to the ground. But the elevation is actually the third component to give a three-dimension exact location.
There are 180 latitudes from 0° to 90° north to 0° to 90° south (Equator = 0) and 360 longitudes (meridians) from 180° in east and 180° in west. The zero meridian was defined in 1883 as Greenwich UK.
There are three ways in giving these coordinates:
In decimal degrees: hddd.dddd° e.g. N25,1418167° ; E055,1853833°.
In degrees and decimal minutes: hddd°mm.mmm (one degree equals 60mins) e.g. N25°08.509; E055°11.123.
In degrees, minutes and seconds: hdd°mm’ss.s (60secs equal one minute) e.g. N25°08’30.54 ;E055°11’07,38.
UTM system
The UTM (Universal Transverse Mercator) system is based on a metric Cartesian grid laid out on a conformal projected surface to locate positions on the surface of the Earth.
The latitude longitude format has the disadvantage of distance between the longitudes decreasing from the equator to the pole since the earth is round. To avoid distortion, grid projections on defined areas were developed where all lines are parallel or in a 90° angle. Therefore the grid has a mesh of equal-sized squares so that the distance between the grid lines can be given in metres or kilometres. You will be familiar with these grids from paper maps. The challenge is to flatten the globe into planes and avoid distortions. The UTM grid is the most popular and international recognized format and standardising different local grids. It is also defined as the international standard for GPS navigation. The globe is separated into 60 north-south orientated meridians which include six longitudes. In very simple words, the globe is sliced up into 1,197 zones which are defined by the zone number (one of the 60 meridians) and the latitude (limited to 84°N and 80°S since the distortion close to the poles would be too big). There are some more irregularities, but since we are not using UTM for the magazine and our books, we will not enter further into details. UTM is useful if you use it together with paper maps based on the UTM grid. Since there are no such maps here (at least for public use) we base our navigation on the easy to understand and apply latitude and longitude format. UTMS coordinates are given in grid zones with the length and height coordinate value (easting / northing)
MGRS
An example of an MGRS coordinate or grid reference would be 40R CN 12346789, which consists of three parts:
– 40R (grid zone designator, GZD),
– CN (the 100,000meter square identifier), and
– 1234 6789 (numerical location; easting is 1234 and northing is 6789, in this case specifying a location with 10 m resolution). (Coordinates with a resolution up to 1m are given 12345 67890)
There is one more thing which might be confusing especially if you work with paper maps. Since UTM, as mentioned, might not be adaptable for all maps, other grid systems might be used. To be able to use the map accurately with the GPS, the GPS needs to adjust to the map. Datums are giving these references. The scientific base for this referencing system is again very complex and it’s enough to know that if you work with GPS and paper maps, you need to ensure that the datum on the map and the GPS matches (don’t confuse datum with date, there is no relation between it even if the words might indicate it).
With the introduction of the GPS as an international standard, the World Geodetic System 1984 (WGS84) was also introduced. This makes it much easier since most modern maps are based on WGS84. So if your GPS is set to WGS84 (as it should be) generally you should be fine if you enter coordinates extracted from a paper map. But you should double check with the map especially if it’s an older version or country specific map (e.g. there are maps in Switzerland based on the CH-1903 datum).
Lastly, in case you recognise that entered coordinates seem to be wrong, check the datum. Most GPS tracker for car devices have more than 100 different map reference systems (datums) installed. If you copy route files on the computer or through digital transfer, the datum of the routes is usually included and will automatically be transferred into your coordinate system.
In summary, since there are currently no proper or detailed maps (UTM or MGRS) for the region (UAE) available, it is best to use your GPS based on longitude and latitude in degrees and decimal minutes. In case you have other coordinates, you need to change the coordinate system in your GPS settings or you can also convert coordinates online into other formats (check http://www.earthpoint.us/Convert.aspx) but be aware that with conversion some accuracy might get lost and wrong entries may generate completely wrong results. Google maps also shows locations if you enter coordinates in degrees and decimal minutes, if you type them like this: N25°08.509, E055°11.123.
Editor’s Note: This article simplifies many topics to give a very basic understanding. This might lead to false interpretation or misunderstandings. There is plenty more scientific and accurate information available in numerous books or online.
