Consider a photoresist line whose cross-sectional profile has a trapezoidal shape with a sidewall angle θ (near 90º) with respect to the wafer surface. if the resist has vertical and horizontal etch rates rv and rh, respectively, derive an expression for the rate at which the critical dimension (horizontal width) of the resist feature decreases with etch time.

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. 

Umm, its not your fault, and its because some things in your brain.