When aligning a third party layer, such as a Cadastre boundary, with our imagery there are only a few possible reasons for any misalignments.
These can be all or any of the following:
- Projection / Datum differences between the two layers.
- Accuracy of the third party layer.
- Accuracy of the Nearmap imagery layer.
- Accuracy concerns for both the third party layer and the Nearmap layer.
- All of the above
You can find information on the accuracy of Nearmap imagery here: Accuracy
Our imagery is by default stored in Web Mercator and is captured with a datum of the date of capture. This means that for our Australian captures in 2020, our imagery was aligned to GDA2020.
If you bring our imagery into your layer via Web Mercator, it is easy to assume that they are in the same projection and datum. As web mercator does not have its own datum component to the projection, however, it is possible that the cadastre boundary could be set with an origin point of GDA94 whereas our imagery might have the origin point of GDA2020 (depending on the date of the capture). This means there would that there will be a misalignment between the two layers by almost two meters.
You can fix this by reprojecting both layers to a local projection.