Site data checklist: before you start the design model

Before the first surface goes into Civil 3D or the first layer loads into QGIS, run a short data-preparation pass. Confirming the coordinate system, the format and the currency of each dataset up front saves the rework that happens when a TIN sits ten metres off the cadastre or elevation comes in on the wrong datum. This checklist groups the work into four stages: decide what you need, pull it in the right format, check it before you build, and hand it on. Work through it in order.

Stage 1: decide what you need and in what format

• List the datasets the task requires. For early site set-up that is usually cadastre (lot boundaries), a ground surface (contours or a DEM), and often imagery for context. A desktop review may need only cadastre and elevation. Do not pull everything by default.
• Match the format to the software and the purpose. Vector datasets (cadastre, contours as lines) export as DXF, Shapefile, GeoPackage or KMZ. Elevation surfaces do not: a DEM comes out as GeoTIFF raster, a TIN surface as DXF, and imagery as georeferenced JPG with a KMZ overlay. Pick per dataset, not one format for the whole job.
• Decide contours or DEM for the surface. Vector contours drop straight in as design linework; a raster DEM is better for slope and catchment analysis and for building a TIN. The trade-offs are set out in Contours or DEM? Choosing between vector contours and raster elevation for site set-up.
• Choose the contour interval before you export. For a flat suburban infill lot a 0.25 m or 0.5 m interval reads the fall; for a large rural parcel 1 m keeps the file usable.

Stage 2: pull the data with the right reference frame

• Set the coordinate system for every dataset. For QLD, NSW and VIC that is MGA2020 (or the matching GDA94 zone for older data) for horizontal, and AHD for heights. A file with no defined projection is the most common cause of misaligned layers.
• Confirm the correct MGA zone for the site. Brisbane and most of SEQ sit in Zone 56; Melbourne and most of Victoria in Zone 55; Sydney in Zone 56. Getting the zone wrong shifts the site hundreds of kilometres. The datum and zone detail is covered in Getting the coordinate system right: MGA2020, GDA94 and AHD for QLD, NSW and VIC site data.
• Keep the vertical datum explicit. Elevation should be in AHD metres. Note it in the file name or a sidecar so nobody assumes ellipsoidal heights later.
• Export cadastre and elevation clipped to the same extent. A single site boundary or buffer means the surface and the lot lines cover the same ground, with no stray parcels or blank raster edges.

Stage 3: check the data before you build the model

• Load cadastre and surface together and eyeball the fit. Lot boundaries should sit where the ground features suggest. A consistent offset across the whole site points to a datum or zone mismatch, not a survey error.
• Check the contour range against known ground. If a lot you know sits near 8 m AHD reads as 800 or as negative, the units or datum are wrong.
• Confirm the surface is a surface, not just lines. A DXF of contour strings is linework until you build a TIN from it. Assign elevations to the correct field before you triangulate.
• Note what desktop data is and is not. Published cadastre and LiDAR-derived elevation set up the model and scope the field work. They are not a survey pickup and not a substitute for a set-out or a site classification. Treat them as the starting frame.
• Watch the common import traps. Duplicate vertices, exploded blocks, and layers landing at the wrong scale all show up on the first import. The recurring ones are listed in Eight mistakes people make importing site data into Civil 3D, QGIS and ArcGIS.

Stage 4: document and hand it on

• Record the source and currency of each dataset. Note where cadastre and elevation came from and roughly when the LiDAR was flown, so the next person knows how fresh the surface is.
• Keep the reference frame with the files. State MGA zone and AHD in a short read-me alongside the DXF, Shapefile, GeoPackage or GeoTIFF.
• Bundle formats to suit the recipient. A drafter on Civil 3D wants DXF and GeoTIFF; a GIS analyst wants GeoPackage or Shapefile; a reviewer without CAD wants the KMZ to open in Google Earth.
• Re-clip if the site boundary moves. If the extent changes, pull the datasets again to the new boundary rather than trimming stale files.

When the reference frame, format and extent are all confirmed, the model builds cleanly the first time. Export site data for any address in the format each dataset supports, or see a sample export to check the structure before you commit.

LayeredGeo lets you download QLD, NSW and VIC site data - contours, cadastre and more - in DXF, Shapefile, GeoPackage, KMZ and raster formats, ready for Civil 3D, QGIS and ArcGIS.

About this article. Published by LayeredGeo. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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