First, a key point about power stations — Page 229, Lesson 213

Let's pick this up right where the material sits — we're in the middle of a list of visual features you use for map reading, and I want to make sure you've got the full picture of what stands out and what can fool you. First, a key point about power stations. They stand out well, but remember they're often located along rivers, and there may be several power stations along a particular stretch of river. So if you see one, don't assume you've positively identified your position — check for the next one and the river itself. Airfields stand out well by day from heights above 1000 ft AGL — that's "above ground level," meaning your height above the terrain directly beneath you, not your altitude above sea level. But always be aware whether the airfield is active or not. An active airfield is a living, moving feature; a disused one is just a mark on the ground. At night, airfield identification beacons are readily visible — those are the rotating or flashing lights that identify the field. Quarries stand out particularly well — the excavation and spoil heaps give strong contrast. But check NOTAMs for blasting activity. NOTAMs are "Notices to Airmen" — official notices of hazards or changes affecting flight. Blasting means there could be debris or dust, and you don't want to be near that. Monuments, follies and chalk cuttings are precise features but rarely lit. A folly is a decorative building with no practical purpose — but it's a fixed, identifiable point. Chalk cuttings are the white scars where a hillside has been cut through, often for a road or railway. They're precise because they're sharp and distinctive, but they're rarely lit, so they're a day-time feature. Lighthouses are excellent features by day or night, but they are not unique unless identified in relation to coastal features by day, or by their correct light transmission characteristics by night. That's a critical point — a lighthouse is only a reliable fix if you can tie it to the coastline by day, or if you know its specific light pattern — the colour, the flash sequence, the timing — by night. Otherwise, one lighthouse looks like another. Now, the second part of this passage moves into something different — visual navigation hazards. These are meteorological or geographic circumstances that can lead to increased flight safety risks through visual illusions. The full treatment is in the Human Performance syllabus, but here's the summary. In less developed areas — deserts, jungles, tundra or snow fields — usable features may be widely separated or even non-existent. And there's a second problem: topographical maps of these areas may be incomplete. So your chart may not show you what's actually there. Then there's the snow and ice scenario. When you have snow and ice from horizon to horizon, and the sky is a uniform layer of clouds so that no shadows are cast, the horizon disappears — Earth and sky blend together. In that situation, and in "white-outs" caused by blowing snow, distance and height above ground are virtually impossible to assess visually. You lose your reference — you can't tell how high you are or how far away things are. Finally, there's a subtle trap with poor contrast, particularly over snow-covered ground. It's possible to focus on high ground well ahead of the aircraft and to fly the aircraft to cross that ground with the appropriate clearance — that sounds fine, you're clearing the high ground you can see. But the poor contrast may mask intervening high ground — ground between you and that far feature — over which your clearance may be inadequate. You're aiming at the far ridge, but there's a nearer ridge you can't see, and you might not clear it. So the theme here is: visual features give you position, but the environment can lie to you. Snow, uniform cloud, poor contrast — these remove your visual references and can hide terrain. That's why you cross-check everything and never trust a single visual impression. That's the substance of this passage