Polygon measure (4)
I believe the answer is:
area
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">polygon measure</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for area that I've seen before include "Field of activity or surface" , "'Tract, region (4)'" , "Surface measurement" , "District; locale" , "topic" .)