Water features tend to occupy the lowest ground in any given area — Page 229, Lesson 210

I want to walk you through the visual navigation features you'll use when flying at low level. Let's start with water features. Water features tend to occupy the lowest ground in any given area. That's important because when you're flying at low level, small water features — a pond, a narrow stream — may be hidden from view by surrounding high ground. Small rivers are often tree-lined. That tree line can help you by providing contrast against the surrounding terrain, making the river easier to spot. But it can also hinder you: if every small river in the area looks like a green line of trees, identifying which particular river you're looking at becomes more difficult. Now, mountains and hills. These can make excellent visual navigation features. But I need to be very clear: flight in hilly or mountainous terrain must only be undertaken after due consideration has been given to safety aspects. That's a professional requirement, not a suggestion. In general, terrain features with good vertical extent — meaning they rise noticeably above the surrounding ground — are more useful for navigation at low altitudes. They're also more dangerous, because they're obstacles. Isolated hills provide the best features: a single hill standing alone is easy to identify and use as a checkpoint. Terrain that undulates fairly uniformly — rolling hills with no standout peak — is difficult to use unless additional features are available to help you pinpoint your position. Valleys tend to be good visual navigation features because you can normally identify them from their orientation — the direction they run — and from the presence of other cultural features inside them. Roads, railways, and towns in a valley offer the opportunity for many precise checkpoints. Let's move to towns and villages. I want to give you a hard rule here: never overfly built-up areas below 1000 ft AGL — that's Above Ground Level — or below a height from which you could glide clear of the built-up area in the event of an engine failure. You use whichever is higher. That said, towns and villages are useful as general indicators of position. You can use them to locate more precise visual checkpoints. Towns are useful features at night because they are normally well-lit. The same is not true of villages — villages are often poorly lit or unlit, so don't rely on them at night. Finally, roads. Motorways and major roads can provide excellent check features by day and by night. Even if there is no discernible checkpoint available on the road itself — no junction, no landmark — the road itself is a line feature. That means you can use it for a track check: are you flying parallel to it, or crossing it where you expected? You can also use it for a timing or groundspeed check: fly a known distance along the road, time it, and calculate your groundspeed. Generally, precise checkpoints can be found at regular intervals along these features — crossroads, motorway junctions, and service stations. Those give you exact fixes along your route.