|STDI Consulting Inc.|
Mississauga Ontario, Canada
|First published on April 25, 2011 |
Last revised on January 05, 2019
|GPS and UTM map grid reference system|
How to convert between GPS coordinates and the UTM map grid reference system
April 2011: Last summer we we had a good time on the lakes and trails up at Algonquin Provincial Park. Last summer refers to 2010, a time when smartphones just started to get smart. Our Garmin car GPS and the Algonquin Provincial Park Map were our sources for planning trips and excursions. But they were not compatible. The Algonquin Canoe Routes Map shows a grid at the scale of 1:126,720 (1 inch = 2 miles).
The car GPS Longitudes and Latitude based on the geographic coordinate system, taking the spherical shape of the earth into consideration. The Algonquin Provincial Park Maps is flat and uses the UTM coordinate system, taking the two dimensions of a paper into consideration.
If you are not much interested in the details of UTM system and need the conversion done on-the-fly, buy a handheld GPS that does the conversion for you. You can find up-to-date information by searching for 'handheld gps units with UTM coordinates'. You may also want to pay attention to the Geocaching feature. I never hunted for a treasure yet, but I like the concept.
Don't count on your cell phone. You may have a GPS enabled phone, but you may not have reception. If you don't turn off the phone when you leave civilization, the battery may drain in just a few hours due to searching for a cell tower. Some older phones may require a cell tower connection to get a GPS lock. No matter what, you will need a map that goes with the GPS coordinates. And for that, make sure you downloaded the maps ahead of time and saved it on the device.
If you didn't run out yet to buy a GPS and are still reading, here we go.
First, how accurate are GPS? Garmin states that they are accurate within 3 - 5 meters. It is also important to know that the GPS signals have to lock in which takes time. Don't move your GPS unit for at least 20 seconds. Keep in mind that your body will block some of the signals.
If you compare the results from several units, take the average. When I did some tests in the backyard over several days back in 2011, exact same location and height, the results were different within about 3 meters on the same device, and up to 25 meters between different devices. And don't pay too much attention on the altitude, this number is way out, the units show differences of up to 50 meters. They claim that this will change in 2018 when a new GPS chip will become available. Give it some time until they are used in phones.
With these 'rounding' differences in mind, we need the GPS coordinates with max 3 digits (eg N45 33.869 W78 33.134) or max 5 digits in decimal (eg Latitude: 45.56448 Longitude: -78.55223). Changing the last digit in the coordinates will move you about 1 meter on the map (after converting to UTM). One square on the map is one kilometer, on the 1:40,000 map, that's 1 inch = 1 kilometer. For practical purposes, a 25 meter discrepancy between devices is not going to make a difference when finding your favourite spot on the map. That's half a millimeter on the map.
Lets have a look at the Algonquin Provincial Park Map. You can buy them in the park.
The UTM system is based on a zone and a Map Datum. This information is printed somewhere on your map. This map here is from Zone 17 and uses the Map Datum NAD 27.
Somewhere on the map you'll find the base numbers for the coordinates (see below). Make sure you adjust the base number correctly, the 7 00 000 translates to 6 99 000 and counting down to the left of it.
Easting: The gate is @ 70 + 4 as per grid (the 4 is 400 meters). Prefix this with the 7 (actually 6 because it's counting down) from the base number on the map. The final Easting is 6-70-4-00 = 670400.
Northing: The prefix is 50 plus the 34 + 2 from the grid. The final number is 50-34-2-00 = 5034200.
Now enter this number in a converter such as the one listed below from Montana State University & Yellowstone National Park and you get the coordinates. To verify, enter these coordinates in google maps.
Converting between systems
The conversion tool I like most can be found at Research Coordination Network. The input form supports the different formats for the coordinates in degrees and decimal.
Look for an app that can convert the GPS to UTM, they are available for Android and iOS.
Algonquin Park Coordinates
As I mentioned in the beginning, my interest for GPS and maps started when we were in our canoe in the middle of the Algonquin Hailstorm Creek. We had the GPS coordinates but no clear reference to pinpoint our location on the map. After all, it's one big marsh and the passage with flowing water changes possibly every year. If you are looking for the Algonquin GPS coordinates, please get them from my Algonquin Park GPS Coordinates posting. I have the coordinates for all major Algonquin points.
January 2019: Technology changed over the past eight years. What didn't change is that smartphones are only as smart as the closest cell tower. There are some apps available today that will work from maps that were previously downloaded and saved. Now you have your offline map available, but not enough battery power to actually use them. Make sure you are prepared for the trip beyond the cell tower and charging station. After all, that is one of reasons we love the outdoors.