1.3.3 Distortions in Mapping

We have already seen in the Geodesy section above, that by modelling the Geoid using an ellipsoid, we have already introduced some distortion in the way that the Earth is represented. Without adjustment, that distortion increases as we proceed further from the point of origin where the datum was established. However, with a well-established datum, these distortions can be minimized. When we make calculations from the Earth’s surface to a flat (projection) surface, we introduce an additional set of distortions. These are in area, shape, scale and azimuth.

These distortions:

• Can be calculated and understood, but without proper care and well educated workforce, it is easy to make mistakes.
• Are non-linear; that is to say, the size of the distortion varies across the projected area are very important component in mapping wellbores.

The most important and potentially destructive distortions when projecting geospatial data to a map are scale and orientation, particularly when mapping wellbore positions. Below shows a ‘macro’ level example of scale and azimuth distortion. This effect happens even at short distances but not so obviously to the eye. The orientation or azimuth change is what is called convergence. Its value can be calculated and applied to ‘real world’ measurements to adjust them to projection north referenced value. Similarly scale distortion can be applied to survey measurements to represent a scaled distance on the map.