Conventional projection
Also called: Mathematical projection · Topic: Map Projections · NCERT: Class 11, Ch 4 "Map Projections"
Meaning
A conventional projection is built wholly from mathematical formulae. It is also called a mathematical projection. No light is shone and no shadow is cast, so it has little link to any projected image. Mapmakers use formulae to give the map a property they want, such as true shape. They could not get that property just by throwing a shadow onto paper.
Example
Mercator's projection, made by Gerardus Mercator in 1569, is the best-known conventional projection. The gap between its parallels is calculated so that it widens towards the poles by exactly as much as each parallel is stretched. Because of this, shapes of small areas stay true, and a straight line on the map keeps one constant compass bearing.
Don't confuse with
- Perspective projection: this is drawn by casting the shadow of the globe's graticule from a light source onto a surface. A conventional projection uses no light source at all.