Translated 20a-Geospatial_Spherical-Lecture. Closes #397.
Updated according comments from @jcarlosgarcia and @juancarlosfarah. Refs #397.
Minor edits. Refs #397.
Merge pull request #423 from puentesarrin/issue-397

Translated 20a-Geospatial_Spherical-Lecture. Closes #397.