First, we ask: why do we even use conical charts — Page 330, Lesson 297

I want to walk you through Chapter 21 of your navigation syllabus — it's all about conical projections, and specifically the Lambert Conformal Chart, which is one of the most important charts you'll use as a professional pilot. Let's start with the big picture. This chapter is called "Lambert's Conformal Chart - 1," and it opens with a series of section headings that lay out the logical flow. First, we ask: why do we even use conical charts? Then we get the background to the Lambert projection itself. From there, we look at the simple conic projection — first its convergence properties, then its scale behaviour. That sets the stage for the real topic: Lambert's Conical Orthomorphic Projection. We'll cover Lambert chart convergence, the fact that it's a non-perspective chart, and then the full list of Lambert chart properties. Finally, there's a summary of all those Lambert properties. So the key idea here is that we're moving from a simple cone wrapped around the Earth to a much more sophisticated version — the Lambert projection — that has specific properties making it ideal for aviation navigation. The chapter title tells you this is the first part of that study. Let me define the terms you'll need right from the start. A conical projection means we imagine a cone placed over the Earth, and we project the Earth's graticule — that's the grid of parallels of latitude and meridians of longitude — onto that cone. Then we unroll the cone to get a flat chart. The simple conic projection is the basic version of that idea. The Lambert Conical Orthomorphic Projection is the refined, professional version — "orthomorphic" means it preserves shape locally, which is critical for navigation because angles measured on the chart match angles on the Earth. Now, convergence is a key property we'll study. On any chart that isn't a simple cylindrical one like Mercator, the meridians don't stay parallel — they converge toward the pole. The amount they converge depends on the latitude and the type of projection. The simple conic projection has a specific convergence pattern, and the Lambert projection has its own, which we'll derive later. Scale is the other big property. On a simple conic projection, scale varies as you move away from the standard parallel — the parallel where the cone touches the Earth. On the Lambert projection, scale is controlled much more carefully to keep distortion low across the whole chart. The heading "Non-perspective Chart" is important. A perspective projection is one where you imagine a light source at a specific point — like the centre of the Earth — casting shadows of the graticule onto the cone. The Lambert projection is non-perspective: it's mathematically constructed, not simply projected by geometry. That means we can tune its properties mathematically to achieve conformality — preserving angles — across the entire chart. So in summary: we start with the simple cone to understand the basic ideas of convergence and scale, then we upgrade to the Lambert projection, which is orthomorphic (conformal), non-perspective, and has carefully defined properties that make it the standard for en-route navigation charts in aviation. The chapter will walk through each of those properties in detail, and we'll end with a summary you can use for reference. That's the roadmap for Chapter 21. Let's move into the first section — why conical charts are used in the first place.