Why can friction make observing newton's first law of motion difficult?

The law says things travel in a straight line at constant speed unless acted upon by a force.  But friction is a force but it can't be seen easily other than its effect, which is to bring the object to rest in seeming violation of the 1st law.

Answer choices? if there is any

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.