Topographical Maps and Map Reading — Page 229, Lesson 212

I want to walk you through some more visual navigation features that you'll use when reading a topographical map and matching it to what you see out the window. Let's start with minor roads. Minor roads make less reliable check features than major roads, but they can still be significant in areas of open country and barren mountainous terrain. The good general guideline here is simple: the bigger the road, the better for navigation. So if you have a choice, always pick the larger road as your visual checkpoint. Now let's talk about railways. When you're flying near large towns or industrial areas, it can be difficult to identify particular railway lines because there are so many tracks crossing each other. But in more open areas, railway lines are excellent visual line features. They can provide precise checkpoints at junctions, at stations, or where there are conspicuous bridges. There's one important limitation you need to remember: railway lines are not normally visible at night. So don't plan to use them as a night navigation feature. Next, woods. The usefulness of woods as visual check features is variable. In general, the rule remains 'the bigger, the better'. Large woods often have distinctive shapes if you're flying above 1000 feet AGL — that's Above Ground Level. But their shapes are often difficult to recognize from lower levels, particularly in hilly terrain. So if you're down low in the hills, don't count on a wood's shape to be clear. There are two more things to watch out for with woods. First, woods change shape due to felling and planting programmes, and this particularly applies to coniferous plantations — those are fir forests. A wood that was a perfect triangle on your map last year might have a chunk missing this year. Second, woods are susceptible to seasonal contrast changes. Snow-covered trees do not contrast with snow-covered fields — everything looks white and the wood's shape disappears. But on the other hand, snow melts first on the trees, and when that happens, the shape and contrast are actually enhanced. So use woods with care; they're not always reliable. Finally, let's cover other features. Many other features can provide excellent precise visual checkpoints. Power stations or isolated factories can often be seen at great range. They often emit steam or smoke, which aids identification and also facilitates estimation of surface wind velocity. If you make use of this, remember that the wind veers and increases with height above the surface. Also remember that power stations are often located along rivers, and there may be several power stations on the same river, so make sure you identify the correct one.