The role of volunteered geographic information towards 3D cadastral systems

Abstract

General mapping, and particularly cadastral mapping, is a highly expensive activity and many governments are no longer willing to continue covering the even increasing costs of surveys. As far as Portugal is concerned – our ultimate field of interest – ongoing 2D property cadastre surveys have revealed to be rather complex, laborious and expensive given Portugal’s territory tissue with a few millions of rather small real estates scattered across a rather irregular topography. Accurate collection methods of even more detailed cadastral data towards 3D cadastral systems are required. Practical acquisition of such data in the field for the purposes above constitutes the main question raised in this paper. It is believed that issues above could be tackled, at least to some extent, by considering Volunteered Geographic Information (VGI). At a time with increasing demands and when public sector resources are declining, VGI should in fact not be seen as a threat but as a potential opportunity for mapping agencies in all domains. Although a VGI approach may not be suitable yet to totally replace standard accurate methods and technologies, such as those used in full measured cadastral surveys, it is argued that VGI may well be considered as an interim step before full surveyed cadastre is eventually achieved. With this regard, a framework consisting of five validity levels of cadastral data is proposed in this paper to be tested and used in a first stage at local government level. VGI was therefore considered and taken into account in designing such framework, whose different levels of validity (in terms of precision and different sorts of accuracy) are fundamentally based on the associate source of information. For the purpose, five possible data sources have been previously identified. The goal of this paper is mainly exploratory in finding potential room in the context of 3D cadastre for VGI to be brought in and how to accomplish it. Future work will entail the identification in more detail of which sorts of cadastral data (2D, 3D or simply descriptive) may be acquired through a VGI approach. Nevertheless, preliminary considerations are drawn on some foreseen sorts of cadastral data that may potentially be acquired with a VGI approach. The design of a participatory web-based application is proposed too.