Subdividing by a legal description is only allowed in instances where planning approval is not required. These exceptions are listed under section 121(2) of The Planning Act, C.C.S.M. c. P80 at web2.gov.mb.ca/laws/statutes/ccsm/p080e.php and section 263(3) of The City of Winnipeg charter.
If it is determined that planning approval is not required for the subdivision, the new subdivision limits must be perpendicular to or parallel with a Dominion Government Survey limit or be the existing limits shown on a registered plan.