Polyconic projection
Topic: Map Projections · NCERT: Beyond NCERT
Meaning
In a polyconic projection, each parallel is drawn as an arc of its own cone. Each cone touches the globe exactly at that parallel. So instead of one cone for the whole map, there are many cones, one per parallel. The map is accurate near its central meridian and grows less accurate away from it. That makes it good for small map sheets that cover a narrow area.
Example
The Survey of India's older topographical sheets used the polyconic projection on the Everest spheroid. Under the National Map Policy 2005, the newer Open Series Maps switched to UTM on the WGS-84 datum.
Don't confuse with
- Simple conical projection with one standard parallel: this uses one cone touching along one parallel. Scale is true only along that parallel and the meridians.