Map projections are transformations between one shape to another, often a 2D surface such as a screen or printout. A selectable pair of projections is shown below, along with a mapping of points - every 10 degrees latitude and longitude - between the two.
This demo is made with D3, Mike Bostock's DOM-based visualization framework. It was adapted, via Albers to Orthographic Projection, from Mercator to Orthographic Projection.