Use complete sentences to describe how measurements of position in two directions (vertical and horizontal) are sufficient enough to describe the position of an object on a flat surface

By using a coordinate system I believe you can find the position of any objects on a flat surface.

If you have an eraser on your table and would like to know its position, you could make your own x and y axis and see in which quadrant your object is in.
your eraser could be 2 units in the x direction (horizontal) and 5 units in the y direction (vertical). 

Now you can use this 'x and y' axis that you have drawn to locate any object. 
If you want to be accurate, you should draw your axes with a meter ruler and choose your point of origin.

Hope I answered your question.