USGS · Map projections (1993)
https://pubs.usgs.gov/publication/70047422
Why flattening the Earth introduces distortion, and why projection choice depends on purpose.

John P. Snyder / USGS · Map projections: A working manual (1987)
https://pubs.usgs.gov/publication/pp1395
Printed pages 41 and 44: the approximate Greenland/South America comparison and spherical Mercator local scale.

Penn State · 2.3 What are Map Projections?
https://courses.ems.psu.edu/geog160/node/1918
Public course material, undated. Equal-area, conformal and compromise projections.

The area comparison is the USGS manual’s approximation. The 60° example describes a local spherical Mercator scale relative to the equator, not the enlargement of the whole island. No course images are reproduced.

Checked 2026-10-02. Undated pages are not assigned an invented revision year.