Ptolemy's model was with the earth fixed in the center of the universe.

The answer to this question would be Geocentric.

In the earlier day before heliocentric found, many people believe that earth is the core of the galaxy. That means the other planet and the sun are moving around it.  This theory was already proven wrong and the theory is now changed into heliocentric which state the sun is the center of the galaxy.

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.