Reading a topo map turns out to be a very useful skill and once you learn how to do it, it's pretty cool how well you can navigate through the backcountry. When we were practicing, we would take turns having a couple people out of the group lead the navigation to get to the next point. I had the incredible opportunity of navigating towards a point that was a little more complicated than figuring out what direction the point is away from where we are, setting our compass to point that way, and walking a bearing straight towards the point. I'd like to show you our trip, explain the basics of reading a topo map, and how we got from one point to another.
First of all, a topo map, or topographical map, is a special map that shows you things like elevation changes, rivers and bodies of water, areas of tree cover or open clearings, park boundaries, power lines, trails, and other useful things that you'd find out in the backcountry. One of the most useful markers are the brown contour lines that denote elevation. Imagine if you were to take a mountain and slice it up horizontally every 40 feet or so, like layers of a cake. If it was a perfectly cone-shaped mountain, if you looked at those slices from above, you'd see concentric circles, like a target or bullseye. The center of the mountain on the map, as seen from above, would be a small circle signifying a peak. Typically, however, mountains are not perfect cones. One thing the contour lines will show you is how steep or flat an area is. If you see contour lines that are very close together, that means that it takes very little horizontal distance to do a lot of vertical distance.. such as the face of a cliff. If you look at the top left on the map, you'll see a steep cliff. We stopped there to have lunch and the view facing north was really nice. :) If you see contour lines that are far apart, that means you have a relatively flat area, like an open field or meadow.
So, with that said, let's look at our setup. We started at point 35 right underneath the world Trail where the trails merge. If you notice, that area is at the top of a mountain, as denoted by the closed circle and concentric lines around the top. Our target was point 5, southeast of point 35. Setting a bearing by figuring out the angle between point 35 and point 5 would work, but if you notice that area of the map is green meaning it's trees and in this case, thick brush. Also, there's a convenient trail we could follow to get closer, rather than trying to bushwhack the whole way there.
Point 5 is slightly on a ridge. If you look at the way the line curves, pointing away from the peak, we can recognize that that's a ridge. If you look juuuust north of point 5, running horizontally you'll see some V-shaped lines pointing left, pointing towards the peak. This is a gulley, like a little valley with land up above you on either side. We decided to try following the trail down to the point that was due west of point 5. If you look at the map, you'll see it slightly turns where the gulley is and we could follow the gulley down towards point 5 and then hop up on the ridge and find the point. The question is.. how far do we walk and how do we know where it is? We want to go the right direction and know how far to walk without going past, you know?
Pulling out our measuring devices, we figured it was about 0.2 miles from where the trails merge near point 35 to where the trail is due west of point 5. Earlier that day we had hiked 0.5 miles on flat terrain and found out that it took roughly 500 paces. (One pace is two steps, right and left.) We also learned that the world mile is based off the word mil, a number that has to do with the number 1,000. Back when the Roman army was around, one mile was basically the distance it took to them to march 1,000 paces. That's where that comes from. So doing a little basic math, we know that every 0.1 miles corresponds to roughly 100 paces. This varies depending upon the length of your stride, if you're going downhill or uphill, how much weight you're carrying on your back, if you're walking on an area like bouldery terrain that requires you to vary the length of your strides, and so on.. but to get a close estimate, you can use pacing to figure out roughly how far you go. So, given that we had measured out 0.2 miles, we knew we had to hike about 200 paces. The plan was to hike down the trail to the point due west of point 5, try and go down the gulley, and get to point 5. When we get there, we would examine how hikeable that terrain was and if it wasn't, we could hike further and try going in from another direction.
So, off we go, walking downhill (notice we're going away from the closed circle) along the trail, mentally counting out 200 paces. The three of us counting paces all stopped at right around the same area. One thing that confused us right away was that the trail did a little S-turn which wasn't shown on the map and so although we were supposed to be heading south according to the map, the compass was showing us heading north. This immediately threw us off and it got a little confusing. Looking around from this area, we were able to find what we thought was the gulley, but it turns out that it was full of thick brush. We later found out that because water tends to flow through gulleys, that area tends to get a lot more plant life and is therefore more difficult to walk through than an open ridge, for example. Since this area was tough to walk through and we weren't exactly sure where we were which made it tough to figure out the exact direction from our current location to point 5, we decided to keep walking down the trail and find an easy to recognize point and set a bearing from there.
Looking back at the map, we saw several options. First, we could keep walking towards the dashed/dotted line that signifies the park boundary. We had seen signposts up earlier off-trail that told us where the boundary of the park was and we figured that if they were out in the backcountry, they'd definitely be along the trail as well. However, if we missed the park boundary, we'd have two catchlines: the north-south trail and the river. If we crossed either one of those two, we'd know we'd gone too far. If we missed the park boundary, we could keep walking to the north-south trail, hike up north that way, and hike in from the east.
So we decided to keep walking and wouldn't you know it, we walked right up to the area where the trails met near the river. It turns out there weren't any signs denoting the park boundary for whatever reason... So, here we are at a junction of multiple trails with a river running east of us. If we took a left and hiked north, we could wind up east of point 5 and hike in from that direction. The trail would curve right a bit and at that point, we could hike west, looking at the landscape and seeing that point 5 was up on a ridge and had a gulley on either side. We could hike up the ridge and find the point. Not only that, but if you notice the map is also white in that area which meant that it was more in a clearing and there would be less plantlife to bushwhack through. It looked like a much easier route than going through the green area.
and so with this we started hiking north. We found the point where the trail started curving right, but we wanted to make sure we knew exactly where we were so that we could set a precise bearing on our compass and walk directly towards the point. It was actually a bit confusing to identify our location, but one guy in our group stepped up with a great idea. He looked around and saw that there was a pretty prominent hill near us northeast of our current location. If you look at the map, east of point 5, along the trail where it starts to curve right, you'll notice a small closed loop northeast of that trail curve that represented the summit of that hill. Sweet!
We then started working out the exact direction that the summit was from our current location. If you draw a line on the map from the little loop towards the trail in the right location, it would then show us exactly where on the trail we were. When we figured that out, we could then figure out what direction point 5 was relative to us and we could hike in that direction.
However, there was a slightly easier solution that our instructor suggested. He suggested that we draw a line on our map between point 5 and that hilltop. That line would cross through the trail. If you look at the map and mentally draw that line, you'll notice that that line would cross the trail slightly north from the curve on the trail where we currently were. What we could do is then figure out that angle and then set our compass to that angle. We'd then start walking north along the trail until our aligned compass pointing towards the summit until the magnetic pointer inside the dial lined up with the angle we wanted. When it did, we knew that we were standing right on the line that goes from point 5 to the peak of the hill. Sweet.
The task then was to simply backsight by aligning the compass with the direction we wanted to go, keeping the summit of the hill 180 degrees behind us, and keeping the compass aligned the whole time.
Once we figured out exactly what direction point 5 was relative to our current location, as well as knowing that the point was up on top of a ridge, we were able to start leap-frogging our way there. Basically we'd send one person out in front and have them walk that invisible line between the summit and point 5 and the person behind them would make sure they're walking the correct line, motioning them to move right or left to stay on line. Following this technique and working out way right up the ridge, we wound up walking right towards the marker! Woohoo!! Success!!
We also had to do declination calculation this whole time. See, compasses work based upon the earth's magnetic field, but it turns out that magnetic north is not the same as true north. The earth's magnetic field actually changes over time and varies depending upon where in the world you are. The magnetic declination in Colorado is currently about 9 degrees east. Back in Georgia it's currently about 4 degrees west. How this affects us is that if you line up north on the map with where the compass is pointing north, they actually won't be pointing the same direction. The compass is going to point slightly off to the side of true north towards magnetic north. The trick is to learn which direction it's pointing and which direction to adjust our compasses and route, whether we should add or subtract that 9 degrees from our bearing calculation. Luckily you get the hang of magnetic declination adjustment pretty quickly and there's some handy mnemonics you can learn to help you remember. Depending on if you're going from magnetic north to true north like reading from the compass to the map, and vice versa, you either add or subtract the magnetic declination value.
Route finding... it's a lot of fun. You take into account lots of variables, and figuring out the best, quickest, easiest, and/or safest way to get from point A to B. There's even a sport based upon route-finding called orienteering and competitions and races where people compete on various difficulty courses to see who can get to all the points the most quickly.
Yeah... fun stuff!!
Oh also, I cooked up a little extra stuff. Google Maps now allows you to get an interactive 3D Google Earth view so you can pan and zoom and change your angle which'll help give us a better idea of the correlation between a topo map and the 3D view you'll find on Google Maps/Earth. Here's the Google Maps/Earth view of this location, and here's an overlay image I created that shows the trails, river, and two points on the 3D map, just to make it easier to jump in and start reading the map on Google Maps/Earth!