S+SNZ Spatial Measurement common mistakes
S+SNZ Spatial Measurement · Understand the traps and how to avoid them.
Calculating site yield or impervious coverage from the whole parcel area while ignoring road reserve, stormwater reserve, setbacks, and other non-developable land.
Candidates default to gross parcel area because it is the most visible number on the plan and they do not separate legal title area from net developable area.
What to do instead
Define and show net site area explicitly: start from legal parcel area, subtract reserves/designations/easements and required setbacks, then calculate coverage and yield from that figure.
Assessing a proposed activity only against the district plan and missing a separate regional rule for earthworks, stormwater discharge, or coastal disturbance.
Candidates treat resource management as a single-plan check and do not scan for overlapping regional, national environmental standard, or designation controls.
What to do instead
Build a consent checklist that tests district, regional, and national instruments separately, and record each applicable rule and consent trigger before concluding permitted status.
Setting out design coordinates directly in the field without transforming them to the survey control datum and checking the combined scale factor.
Candidates assume design CAD coordinates and survey coordinates share the same origin and scale, especially when both are labelled in metres.
What to do instead
Establish the project control datum, apply the documented transformation and combined scale factor, and verify setout by checking residuals against at least two independent control points.
Reporting GNSS-derived ellipsoidal heights as reduced levels without applying a geoid model.
Candidates see a height in metres from the receiver and treat it as equivalent to an orthometric height above mean sea level.
What to do instead
State the height type explicitly, convert ellipsoidal height to orthometric height using the correct geoid model and epoch, and quote the datum and uncertainty.
Treating a GNSS position as conclusive boundary evidence without reconciling it to the cadastral survey dataset, survey plan vectors, and existing boundary marks.
Candidates equate coordinate accuracy with legal boundary position and skip the plan reinstatement process.
What to do instead
Reinstate the boundary from the official survey plan and marks first, then use GNSS only as supporting evidence; document the plan, parcel appellation, and any discrepancies.
Reducing soundings to chart datum by applying a tide correction to mean sea level or by using the wrong sign for the tide height.
Candidates confuse chart datum, mean sea level, and the tide-gauge zero, and they apply corrections mechanically without checking the datum relationship.
What to do instead
Use a documented reduction workflow: identify chart datum for the survey area, apply tide and transducer draft corrections with explicit signs, and verify against a known check line or benchmark.
Overlaying GIS layers without explicitly setting the coordinate reference system and datum transformation, assuming all data are in the same CRS.
Candidates trust layer display in the GIS and do not check metadata, axis order, or whether NZGD49 and NZGD2000 data have been mixed.
What to do instead
Inspect and set the CRS for every layer, apply the correct datum transformation, confirm axis order, and run a control-point check before analysis.
Using a measured ground distance as a grid distance, or vice versa, without applying projection scale factor and elevation factor.
Candidates treat distances in the projection plane and on the ground as interchangeable because both are expressed in metres.
What to do instead
Label every distance as ground, ellipsoidal, or grid; apply the combined scale factor in the correct direction and show the reduction in the calculation.
Computing a traverse closure by distributing misclosure without first checking angular misclosure against the allowable tolerances and identifying the source of error.
Candidates rush to adjust coordinates and treat the traverse as a purely arithmetic exercise, masking a gross angular or linear error.
What to do instead
Compute angular misclosure first, compare it with the specified tolerance, investigate any outlier, then adjust linear misclosure using a stated method and report the final residuals.
Mixing angle or bearing conventions in calculations, such as entering degrees-minutes-seconds as decimal degrees or using quadrant bearings where azimuths are required.
Candidates switch between field-book notation, calculator entry, and CAD conventions without converting or labelling the convention being used.
What to do instead
State the angular unit and bearing convention at the start of each computation, convert all entries to one convention, and perform a back-bearing or closing-angle check before finalising.