The sinusoidal projection is a type of map projection known for preserving the relative sizes of land masses across the map.
Understanding the Sinusoidal Projection
The sinusoidal projection is a pseudocylindrical equal-area projection displaying all parallels and the central meridian at true scale. This means it's designed so that areas on the map are proportional to the corresponding areas on Earth, which is a key feature of "equal-area" projections. It achieves this by using straight lines for parallels (lines of latitude) and a straight central meridian (line of longitude), but the other meridians are curved, creating the characteristic sine-wave shape (hence "sinusoidal").
Key Characteristics:
- Pseudocylindrical: It's not a true cylindrical projection but resembles one with parallels as straight, parallel lines.
- Equal-Area: Preserves area sizes, making it suitable for thematic maps showing spatial distribution (like population density or land use).
- True Scale: The distance along any parallel and along the central meridian is shown at true scale (or a constant scale factor relative to other areas on the map).
Distortion:
While it preserves area and maintains true scale along parallels and the central meridian, the sinusoidal projection introduces shape distortion. As the reference states, the boundary meridians bulge outward excessively producing considerable shape distortion near the map outline. This distortion is minimal near the center of the map (along the central meridian) but becomes significant towards the edges, especially in the higher latitudes.
Practical Implications:
- Often used for mapping continents or countries that are wider than they are tall, as distortion is less severe in the east-west direction near the equator.
- Useful for thematic maps where accurate area comparison is crucial.
- Less suitable for navigation or maps where true shape or angle preservation is important (unlike conformal projections like Mercator).
In essence, the sinusoidal projection offers an equal-area view of the world, prioritizing accurate representation of size over shape, particularly noticeable as you move away from the map's center.
