What is the primary difference between a geographic coordinate system and a projected coordinate system?

The primary difference between a geographic coordinate system (GCS) and a projected coordinate system (PCS) lies in the way they represent locations on the Earth's surface. A geographic coordinate system defines positions based on a spherical framework, using latitude and longitude to express coordinates. This system is inherently three-dimensional, as it reflects the Earth's curvature.

In contrast, a projected coordinate system transforms this spherical representation into a two-dimensional flat surface. This process is known as map projection and allows for more practical use in mapping and spatial analysis by enabling measurements of distance, area, and direction on a flat surface. The projection introduces a way to accurately represent geographic information on maps while accommodating various needs for detail and scale.

The other choices do not accurately capture the fundamental distinction between these systems. For example, while GCS does involve angular units (degrees of latitude and longitude), PCS uses linear units (like meters), making the first choice misleading. The idea that GCS is flat and PCS is spherical is also inaccurate, just as stating that GCS is less accurate than PCS does not encapsulate the core reason for their differences in representation.