Line, row, rank, file, echelon, tier are comparable when meaning a series of things arranged in continuous or uniform order.
Line means little more than this, except when it is attached to a specific application that increases its implications; thus, a line of type may equal a line of poetry, but there is a wealth of implication in the second that is absent from the first.
Row may suggest one line or one of several parallel lines; it is applicable to lines composed of persons or of things whether they range horizontally or vertically or abreast or away from one.
Rank and file are found chiefly in military use, rank denoting a row of men side by side, file a row of men one behind another. The conjoined use of these terms in rank and file is an idiomatic extension meaning the masses of men as distinguished from their leaders or rulers.
Echelon usually implies a regular arrangement or formation in which each unit (as one of a series of parallel ranks of troops or one of a fleet of vessels headed in the same direction) is a little to the left or to the right of the unit immediately behind.
Tier applies to one of a set of rows arranged one above another; it occasionally refers to persons but usually deals with parts of a structure or framework which are repeated.