Line on a map (7)
I believe the answer is:
contour
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">line on a map</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for contour that I've seen before include "Silhouette" , "Line on map indicating height" , "Outline, profile" , "Feature on map" , "Defining line" .)