Topographical Maps and Map Reading — Page 229, Lesson 207

I want to walk you through the very heart of visual navigation — map reading. This is the skill that turns a chart into a picture of the world outside your windscreen, and it's the foundation of everything we do when we navigate visually. Let's start with the definition, because it's precise and it matters. Map reading is defined as visualizing the physical features of the ground as represented on the map by symbols, and forming a mental picture of the ground by relating the features one to another. So you're not just looking at a symbol and saying "that's a river." You're building a mental model — you see the river, the road crossing it, the hill behind it, and you relate them to each other. That relationship is what gives you the picture. Now, there are two directions this process can go, and they're used in different situations. The first is called reading map-to-ground. This is the basic technique, and you use it when you're confident that you are near track and near on-time. You have the map, you know roughly where you are, and you look from the map out to the ground — you find the features on the map and you match them to what you see outside. The map leads, the ground confirms. The reverse process is called reading ground-to-map, and you use this when you're less certain of your position. Here you see an arrangement of features on the ground first — a distinctive pattern of fields, a railway, a bend in a river — and you search the map to find that same arrangement, and that locates you. The ground leads, the map confirms. So the direction of the reading tells you how confident you are: map-to-ground when you're sure, ground-to-map when you're not. Now, visual navigation using map reading is a skill. It needs practice, and it will develop with experience. But there are factors that make the task easier, and the most important of these are thorough flight planning and preflight route study. You don't start this in the air — you start it on the ground, before you even get to the aircraft. In flight, there are three priorities that sit alongside the navigation. First, try to remain on track and on time, and if you go off track, regain track as soon as possible. But — and this is a critical point — do not concentrate too much on navigation alone. It is equally important to keep a good look-out to reduce collision risks, to be aware of any potential weather problems, and to manage the aircraft systems. Navigation is one task among several, and you must balance them. Now let's talk about visual checkpoints, because this is where the planning becomes concrete. In the planning stage, the pilot studies the route and selects visual checkpoints, normally occurring at about 5 to 10 minute intervals. So roughly every five to ten minutes of flying, you should have a checkpoint coming up. What is a visual checkpoint? It's a significant ground feature which can be overflown, or used as a reference to fly an appropriate distance away from. So it's either something you fly directly over, or something you offset from — you fly a set distance abeam of it. Ideally, the checkpoint should be recognizable from some distance away, and that's important because it allows for timely alterations of heading. You want to see it coming early, so you have time to adjust your heading smoothly, not scramble at the last second. And here's a subtle but very practical point: visual checkpoints do not need to be exactly on track. A good feature close to track is better than a poor feature on track. So don't force yourself to use a weak, indistinct feature just because it sits right on your line. A strong, obvious feature slightly off track is far more useful — you can use it as a reference and fly an appropriate distance away from it. So to pull it together: you plan your checkpoints at five to ten minute intervals, you choose significant features that you can see from a distance, you prefer good features near track over poor features on track, and you read the map in the direction that matches your confidence — map-to-ground when you're sure of your position, ground-to-map when you're not. And all the while, you keep your look-out, your weather awareness, and your systems management in balance with the navigation.