Fix typo spotted by @MCHU-1999

Fixes #55

topofeatures/topofeatures.tex

@@ -246,7 +246,7 @@ \subsection{Curvature}%
 If there is no contour segment, then $v$ is either a peak or a pit.
 A peak will be profile and plan convex; a pit will be profile and plan concave.
 
-If there are 2 segments, then we can use these to estimate the direction of the aspect, it will be perpendicular (thus the bisector between the 2 segments is a good estimate) in the direction or lower elevations.
+If there are 2 segments, then we can use these to estimate the direction of the aspect, it will be perpendicular (thus the bisector between the 2 segments is a good estimate) in the direction of lower elevations.
 If we simply look at the elevations higher and lower than $v$ along this direction, then we can easily verify whether $v$ is profile convex or concave.
 For the plan curvature, we can simply walk along one of the 2 edges so that higher elevations are on our left, $v$ is plan convex if the contour line makes a left turn at $v$, if it makes a right turn it is concave, and if it is straight then it is plan flat.