linear

adjective:arranged in or extending along a straight or nearly straight line
- The students stood in a linear formation for the photograph.
adjective:progressing from one stage to another in a single series of steps; sequential
- The story followed a linear progression, moving from start to finish without jumps in time.
adjective:describing a relationship between variables that change in one variable produces a directly proportional change in another
- There is a linear relationship between the force applied and the acceleration of an object.