The UTM Coordinate System


As a member of a search team, either in the field or command post, there are many ways to report or find your position.  You will all want to be on the same page, so to speak.  If you have purchased a GPS (Global Positioning System) unit and it is still in the default settings, your GPS is probably set to LAT/LON (Latitude/Longitude).  This is a great system for aviation and maritime use or areas of great flat plains.  Most large scale maps cover an area of 6 degrees of longitude, and LAT/LON coordinates are based on a scale of 1:1,000,000.  In SAR work, we would like a little more detail than that.  Most of the maps that we use in the field are USGS (United States Geological Survey) 7.5 minute quadrangle.  It represents a scale of 1:24,000.  Double check to see which Datum we will be using.  Older maps use NAD 27 (North American Datum 1927).  If the lines for UTM are there, then you just might be using NAD 83.  Today we will be discussing and learning to use the UTM ("Universal Transverse Mercator") system.  We will learn to find where we are as well as where we want to go using this method. This method is fairly simple to learn if you open your mind to it.  We will be using some compass techniques but for the most part, forget what you know (temporarily) and just remember you can teach old dogs new tricks.


What Is UTM?

UTM stands for Universal Transverse Mercator.  But who really cares what it stands for; the real question is where did it come from?  And why?  The UTM system was devised by the Military as the best way to draw the earth, which is round, on a flat piece of paper.  This is a very important note, as GRIDS (we will discuss later) are Perfectly Square. The system is widely used by the U.S. Forestry Department and the Military.  Five main characteristics of the UTM system are very important to remember.

  • Each GRID on the map is square.

  • There are no negative numbers.

  • The East-West units of Measure are the same as North-South units.

  • You will always read left to right and from bottom to top.

  • It is decimal based. No messing with minutes and seconds.

  • It is easy to abbreviate coordinates when working in a small area.


How Does It Work?

The GPS system is very easy to understand.  The handheld unit has a small satellite dish or antenna to receive signals from manmade satellites orbiting the earth at a known location to pinpoint your location.  The unit translates the signals into two long numbers.  Remember, as an expensive and sophisticated as the GPS is, YOU are the one that must know how to plot these numbers onto a topographical map to obtain your position, or you might as well have hiked with a rock for the last ten miles.  If you still don't seem understand how this works let's see if I can explain it  in easy SAR terminology.  Let's look at the handheld GPS unit as a compass (you remember those things that hang around your necks).  Now with our GPS unit we will triangulate (to find a position by taking a bearing using at least two fixed points) using satellites in outer space instead of mountain tops with water tanks.  The GPS unit receives a signal from multiple satellites orbiting the earth at known locations and then uses triangulation to pinpoint your position. 



What Do I Need To Do This?

You don't need an expensive GPS unit to use the UTM system; it just makes it a little easier.  As we all know, we can't afford to purchase a GPS unit for every member.  In fact, even with three or four GPS units, we may not be able to send all teams into the field with their own GPS unit. We would like the whole team to use the same system for ease of operations, the UTM coordinate system, and reporting their position.  So what do we need to use this system?

  • A GPS unit or a compass (I will explain later).  

  • A map of the area

  • A plastic grid.


The Map

Now for the BAD NEWS!  To prepare to read and plot UTM coordinates, you must erase all North and South lines and redraw grids using the blue tick marks.  Newer maps might have these drawn on them for you.  The blue tick marks can be found on the borders of the map.  We will be using the newly formed grid squares to find our location. Each GRID is a 10 unit by 10 unit square (remember the metric system?)

 


This is available from maptools.com in pdf format




Learning To Read

Go ahead and take out your map.  Some new maps printed after 1990 will have the GPS grid printed on them already.  Notice the numbers along the sides where the blue tick marks are; these are the UTM grid coordinate numbers we will be using.  If your map does not have the GPS lines on it, you will have to draw then in using either a pencil or permanent marker.

Along the top you have 321 322 323 324 325 326
Along the side you have 3807 3808 3809 3810 3811 3812

Even though the zeros are not printed, it is implied that they are there.  For example:

Along the top you have 321000 E. 322000 E. 323000 E. 324000 E. 325000 E. 326000 E.
Along the side you have 3807000 N. 3808000 N. 3809000 N. 3810000 N. 3811000 N. 3812000 N.
 

The Numbers along the Top and Bottom are EAST - The Numbers along the sides are NORTH.

Along the Top 323992 Easterly
Along the Side 3807982 Northerly

Now, The Two Golden Rules of Reading UTM coordinates:

  • Read Right and Up or Up and Right

  • Always Report North (Up) Then East (Right)

When we report our position we want to use one 6 digit number.  Three digits for North and Three digits for East. Now look at your Map and find:

 

Along the Top 323992 Easterly
Along the Side 3807982 Northerly

You should be on bottom right quad of the Fillmore California 7.5 map.

To simplify the above coordinates, we would drop the small numbers in the front, report the big numbers plus one small number to the right, and yes you will round out this number.  Now drop the words Northerly and Easterly.  Now you can radio the command post as follows:  Team X is at UTM 080240 

Exercise #1
Read the coordinates and write what you would radio in:

1. 321000 East 3809000 North  
2. 327000 East 3807000 North  
3. 326910 East 3817415 North  
4. 3815100 North 321580 East  
5. 3809790 North 321450 East  

 


Exercise #2

What if you are not conveniently on a grid corner (which is more often the case then not)?  This is where the small plastic grid comes in handy.  Remember, earlier we discussed that each grid is a ten unit by ten unit perfect square. Well, if you lay this transparent grid on the map, you can pinpoint your position to a particular grid square.  So, lets  find UTM coordinates 070270 (Hint: you will not need the transparent grid to find this spot).  You should be in the lower right quad, just south of the fish hatchery.  Now find 134252. upper right quad, you should have the x of the grid somewhere around Oat Mtn.  Remember to read right and up, 325200 East, I count two small squares past 325, and now go up 3813400 North, I count four small squares past 3813.  And to radio this position in it would be 134252, North First then East.

1.  Oak Village                                            
2.  Peak 4676                                            
3.  Coldwater Canyon & Sespe Creek                                            
4.  BM 504                                            
5.  Santa Clara School House                                            


Exercise #3

 Now you think you know enough.  Let's say you have been hiking all day, having fun with the brand new GPS that you received for your birthday.  You're eight hours into your hike and of course you didn't check your battery strength before you left your car, or you dropped the GPS and it is shattered.  Now what?  Now you are carrying that two hundred dollar rock we spoke about earlier.  So now we have to manually find our position.  We use that plastic box with that compact mirror and that spinny needle that you have around your neck.  Now this only works if you have a map of area, and know how to use the compass as a protractor.  You are able to see peak 1552 towards the North and you shoot a bearing of about 8 degrees, then you turn, locate peak 1561 towards the East and shoot a bearing of 72 degrees.  You now go to your map and draw a line from peak 1552 South, Just the opposite (or azimuth) of the North bearing, so the line would be at 188 degrees from peak 1552.  Now find peak 1561 and draw a line from peak 1561 West, opposite (or azimuth) of the East bearing.  It should be a heading of about 252 degrees.  The lines of intersection are where you are.  If we did this right, we should be about 3807990 N. and about 324090 E. or 080240.  Armed with that knowledge, you can find you way back to your car, or even call in a helicopter pick up. The best part of all this, no batteries are required (unless you are using a flashlight to read the map).  So this should teach you to (at a minimum) check the condition of the batteries or bring extra batteries for any electronic gear you might be using.  Carry a map of the area and compass and know how to use them.