Teaching Conformal Projections

I had a small revelation in class the other day while I was teaching projections. I have an inflatable globe I like to carry to reference an actual 3D representation of the earth when my powerpoints only show a flat sphere.

On my way to class, feeling like a geography professor.

Conformal projections preserve the shape and angles of the world, but distort sizes and distances. A tip-off that a projection is conformal is that the meridans and parallels (latitude and longitude lines) are perpendicular for the whole map. This forms a grid. It’s easy to say this out loud and believe that people will get it, but in reality, projections are rather abstract, adn there’s just not enough time in a class to have everyone do their own actual projection to tangibly connect the abstraction to reality.

On my inflatable globe (and on all other spheroid or ellipsoid representations of the earth), lines of longitude and latitude are always at right angles to each other. Just like in a conformal projection.

  1. Student assesses the ellipsoid globe, looking particularly at the meridians and parallels. Prompt: how would you describe the relationship between these lines? Is if the same for the whole world/ellipsoid? What relationships are the same and what are different?
  2. Look at a world-map projection in a specific format. What is the relationship between the meridians and parallels? Which relationships are consistent and what are not?

With little prompting, the fact that the lat/long line angles are always right angles in both conformal projections and on the globe gets “aha!” faces as the concept of round to flat clicks.

Another finding from bringing this see-through globe to class? Holding it in front of the projector makes azimuthal projections. Helpful for linking the round ellipsoid to the flat projection.