Possibility of a Dynamic Cadastre for a Dynamic Nation

Abstract

New Zealand, lying across the Pacific/Australian plate boundary, is subject to ground movements within the country of approximately 5 cm/yr. The existing geodetic control network and datum, New Zealand Geodetic Datum (NZGD) 1949, has been distorted by the effect of this ground movement. Because of these distortions, cadastral boundary coordinates, if held fixed in a coordinate cadastre, would eventually conflict with the position of slowly moving ground marks. However, the use of new technology such as GPS is ideally suited to the development of a coordinate cadastre. A dynamic coordinate cadastre is a possible outcome of recently started projects. A programme is underway to develop a modern control network and new datum (referred to as NZGD 2000) to replace the existing network. This could include up to 30 GPS permanent tracking stations which would monitor the integrity of the new datum and determine rates of ground deformation. A four dimensional (dynamic) datum with coordinates assigned velocities and changing to reflect ground movements is an option. As a separate project, the Department is considering the automation of the survey and land title systems. The automation of the survey system would see the digital capture of land parcel dimensions. Through connection to the geodetic network, geodetic coordinates would be assigned to parcel boundary points resulting in a coordinate cadastre. As the geodetic network moves to reflect ground movements, adjustment for this could be applied to boundary points forming a dynamic coordinate cadastre. In this manner, coordinates of boundary points would encapsulate available evidence of their true ground positions. This would not be a legal coordinate cadastre, but in the absence of other evidence the coordinate could be accepted as evidence to define parcels. To take the model fürther, it is conceivable that the cadastral surveyor in performing surveys would contribute to the geodetic network and dynamic datum. This possible model is debated.