State Plane Coordinates and the Deed That Doesn't Match
A surveyor prepares a boundary survey of a parcel in Arkansas and reports coordinates in the Arkansas State Plane Coordinate System (NAD83). The deed describes the parcel by metes and bounds with a bearing and distance call of N 45°00'00" E, 500.00 ft. The surveyor's GPS-derived coordinates for the two endpoints, when inverse-computed, yield a grid bearing of N 44°58'12" E and a grid distance of 499.94 ft. The surveyor's client compares the survey to a neighboring survey that used a different projection zone and reports a slightly different bearing. The client asks why the numbers don't match the deed exactly.
1. Explain why the grid bearing and distance differ from the deed's bearing and distance, and what the surveyor should report.
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State Plane coordinates are grid values on a map projection; the deed's bearing and distance are ground values (or record values) measured along the ground. The difference arises from the projection: grid bearings differ from ground bearings by the convergence angle, and grid distances differ from ground distances by the scale factor (and, for longer lines, elevation factor). The surveyor should report the record bearing and distance as called in the deed, and separately report the grid coordinates and grid inverse as computed, clearly labeling which is which. The surveyor should explain the convergence and scale corrections so the client understands the difference is expected and not an error. The neighboring survey's different zone may also produce different grid values; the surveyor should note the zone and datum used.
2. The client insists the surveyor 'fix' the coordinates so the inverse matches the deed exactly. How should the surveyor respond?
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The surveyor should decline to alter coordinates to force a match with the deed. Coordinates are derived from measurements and the projection; changing them to match record values would falsify the survey. The surveyor should explain that the deed's bearing and distance are record evidence, while the coordinates are a separate representation, and that the small differences are explained by projection corrections. The surveyor can provide a table showing both record and grid values with the corrections applied, and note the datum and zone. If the client needs coordinates that reproduce the deed, that is a separate product and should be clearly labeled as record-based, not measured.