Topographical Maps and Map Reading — Page 229, Lesson 212

We're now into the heart of map reading — using the ground as your navigation aid. I want to walk you through the visual check features you'll rely on, starting with the ones that are most reliable, and then the ones you must treat with caution. Let's begin with minor roads. These 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 when you're planning, you want to prioritise the larger roads as your primary checkpoints, and treat minor roads as secondary. Now, railways. When you're flying near large towns or industrial areas, it can be difficult to identify particular railway lines — there's just too much clutter on the ground. 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. One critical limitation to remember: railway lines are not normally visible at night. So if you're planning a night flight, don't count on them. Next, woods. The usefulness of woods as visual check features is variable, and I want you to remember that word — variable. In general, the rule remains 'the bigger, the better'. Large woods often have distinctive shapes if you're flying above 1000 ft AGL — that's Above Ground Level, so 1000 feet above the terrain. But their shapes are often difficult to recognize from lower levels, particularly in hilly terrain. There are three specific cautions I want you to hold onto. First, woods change shape due to felling and planting programmes, and this particularly applies to coniferous plantations — that's fir forests. Second, woods are susceptible to seasonal contrast changes. Snow-covered trees do not contrast with snow-covered fields — everything just blends together. But on the other hand, snow melts first on the trees, and when that happens, shape and contrast are actually enhanced. So the lesson is: use woods with care. Finally, let's look at other features. Many other features can provide excellent precise visual checkpoints. Power stations or isolated factories can often be seen at great range, and they often emit steam or smoke, which aids identification and also facilitates estimation of surface wind velocity — that's the speed and direction of the wind at the surface. If you make use of this, remember that the wind veers and increases with height above the surface. So the smoke at the surface tells you the surface wind, but as you climb, the wind direction shifts and strengthens. Also remember that power stations are often located along rivers, and there may be several power stations in the same area — so don't assume the first one you see is the one on your chart. Let me tie this together. Your most reliable visual check features are the big ones — major roads, railways in open country. Your least reliable are the ones that change — woods, especially coniferous plantations, and minor roads in cluttered terrain. And your opportunistic ones — power stations and isolated factories — are excellent, but only if you remember the wind veers and increases with height, and that they cluster along rivers.