Final answer:
A conformal projection is used to project an ellipsoid (3D shape) onto a plane (2D shape), and it preserves local angles and shapes. The Mercator projection is an example of a conformal cylindrical projection.
Step-by-step explanation:
When projecting a three-dimensional ellipsoid onto a two-dimensional plane, the type of projection used affects the properties of the resulting map. The correct answer to what happens when we project from an ellipsoid to a plane using a projection that maintains angles is a) Conformal projection.
Conformal projections preserve local angles and shapes, making them useful for navigation and for maps of smaller areas where the distortion of area is not as significant. An example of a conformal projection is the Mercator projection, which is known for making maps where all latitude lines have the same length as the equator. This is a type of cylindrical projection, where the surface of the Earth is projected onto a cylinder that is then unrolled to create a flat map.
Three other options listed are types of projections but do not describe the property of maintaining angles when projecting an ellipsoid onto a plane. Cylindrical projection refers to the method of projecting, but does not specify the property of angle conservation. Orthographic projection presents a view from an infinite distance, like a camera image. Azimuthal projection projects the Earth onto a flat plane touching the globe at a single point, often used for polar areas.