Plotting UTM Coordinates with a Grid Style Tool

Hi.

John with MapTools.com here to show you how to plot a UTM coordinate from your GPS, onto your map using a UTM Grid tool.

The most common thing I do with my GPS receiver is using it to check my current location on my map.

I pull the GPS out of my pack, turn it on and get my coordinates. With a quick plot onto my map, I’ve confirmed my location, and I’m done with the GPS.

Here is my GPS displaying the coordinate I am going to show you how to plot onto a map.

It’s a UTM coordinate. UTM stands for Universal Transverse Mercator, and that’s the easiest coordinate system to work with in the field. I’ve already set my GPS receiver to display UTM/UPS coordinates, and I’ve told it to use the NAD27 CONUS map datum which matches the map we will be using.

The map I’m working with is a United States Geological Survey 1:24,000 scale topographic map titled Sharktooth Peak, California

If we look at the fine print at the lower left corner of the map. We can confirm that the map has a 1000 meter UTM grid for zone 11, printed on it and that the map is based on the 1927 North American Datum, or NAD27 CONUS on the GPS setup menu.

Most maps of locations in the continental United States will use on of three map datums; NAD27, NAD83, or WGS84. It’s important that your GPS setting match the datum used by your map.

The first step in plotting our coordinate, is to locate the 1000 meter grid square defined by the UTM coordinate.

Let’s look at the UTM coordinate more closely.

The 11S is the zone number and latitude band letter. This part is necessary to make this coordinate a unique location on a global scale. Unless you are working with coordinates that cover a very large area, you can usually ignore the zone.

The remaining top number represents a distance measured from west to east in meters, and is called the “easting.”

The bottom number represents a distance measured from south to north in meters, and is called the “northing.”

To help understand which digits are used to locate the 1000 meter grid square on the map, let’s write the number 1000 below both the easting and the northing.

The digits from the thousands place and larger are used to locate the grid square on the map.

The coordinates indicate that we are in the 1000m grid that begins at three hundred and nineteen thousand meters east and four million one hundred and forty five thousand meters north.

Let’s find the grid square on the map.

Looking at the top edge of the map, starting on the left side, we see the first UTM grid line is labeled three hundred thirteen thousand meters east. The next line to the east has an abbreviated label for three hundred fourteen thousand meters.

We are looking for the three hundred nineteen thousand meters east grid line.

315 … 316 … 317 … 318 …

There it is, Three hundred nineteen thousand meters east.

Our coordinate is located in this 1000m band between three hundred nineteen thousand meters East and three hundred twenty thousand meters East.

Now let’s move to the lower right corner of the map. The first UTM grid line going up the right side of the map is labeled four million one hundred thirty nine thousand meters north. The next line to the north has an abbreviated label for four million one hundred forty thousand meters north.

We are looking for the four million one hundred forty five thousand meters north grid line.

4141 … 4142 … 4143 … 4144 …

There it is, our million one hundred forty five thousand meters north.

Our coordinate is located in this 1000m band between four million one hundred forty five thousand meters North and four million one hundred forty six thousand meters North.

Our coordinate is located in the 1000m grid square where these bands intersect.

Now it’s time to locate the coordinate within the grid square.

If we look at the coordinate again, we see that the point we are interested in is 174m east and 312m north of the western and southern edges of the grid.

We could estimate that distance within the grid. But instead, I’m going to show you how quick and easy it is to use a grid reader.

We are going to use a 1:24,000 scale UTM grid reader from MapTools.com. The 1:24,000 scale of the tool matches the scale of our map, and the tool is designed to work with a 1000m grid square.

Place the tool onto the map and align it with the grid square we just located. Double check that the grid on the tool fits the 1000m grid square on the map

The grid reader divides the 1000m square into 100m squares.

A 100m square is the size of two soccer fields side by side.

We use the hundreds digit from the easting and northing to locate the 100m square identified by our coordinate.

In this case that would be 100m east and 300m north. The 100m grid square we want is at the intersection of the 100m column and the 300m row on the grid tool. Avoid the temptation to round the coordinate to the closest 100m value. That will put you in the wrong 100m square about half the time.

Sometimes you will want to know your location with more precision than just “two soccer fields.”

We can use the 10m digits from our coordinate to estimate position within the 100m square.

For our coordinate that would be 70m east and 10m north.

Each 100m square has a dot in the center 50m from each edge. Use that dot to help estimate position within the 100m square.

The 1m digits in our coordinate represent such a small mark on our map that they are rarely used when plotting.

To place a mark on the map, take a mental snapshot of the point’s location with respect to the map markings, move the tool out of the way, and then make the mark in the correct position.

In many situations you do not need to mark the map. Just visually confirming your location on the map is sufficient.

The UTM grid reader is an easy tool for a beginner to understand and use. But, if you find that you often need more than 100m precision or that you want to be able to more easily make a mark on the map, you should check out the slot style UTM tools from MapTools.com.