One event in a high school track meet is the 400 meter run. if the runners of the 4oo meter event start and end at the same location, what is their displacement?

In physics, displacement is a physical quantity that is used to describe the overall change in the position of an object/person.
In other words, it describes how far you are from your initial position.

In the given problem, the initial position is the same as the final position. This means that overall change in position is zero, which also means that the difference between the final and initial positions is zero.

Based on the above, the displacement is zero.

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero.