It isn't strictly wrong (and we see property descriptions often enough that use "along" in this manner), but it would be better to say "on", as in "on an arc of curve to the left".
In Surveying, the generally-preferred usage of "along" is in situations where two items tend in the same basic direction, but not precisely on top of each other. For example, we might say "N45°00'00"W along a fence line", for a fence that isn't exactly a straight line, and might wander back and forth on either side of a true line, but overall follows the stated course.
Along: Lengthwise of, implying motion or at or near, distinguished from across. By, on, up to, or over, according to subject matter and context. The term does not necessarily mean touching at all points; nor does it necessarily imply contact.
So according to the definition in Black's Law Dictionary, "along" can be used to mean "on", but it does not necessarily mean "touching at all points". But with legalese, it's best to say precisely what you mean, so if you mean "touching at all points", it's better to use the word "on".
