The new, LADM inspired, data model of the Dutch cadastral map

Abstract

The Netherlands’ Cadastre, Land Registry and Mapping Agency – in short Kadaster – provides legal certainty about every piece of land (and water) in the Netherlands. Newly surveyed cadastral boundary geometry is documented in land surveying field sketches and processed in the nationwide cadastral map. Because of the different working methods since the start of cadastral surveying in 1811 (a nationwide cadastral map was available in 1832 when Kadaster was established) the map has a so-called graphical quality. The standard deviation of boundary points is 20 cm for urban areas and 40 cm for rural areas (in the national reference system), this implies that the geometric quality of the current map is insufficient for determining the exact parcel location in the field. With an increasing digitization and open data policy, multiple sources of information (including the cadastral map) are demanded to be accessible and usable by a wide range of users. This so-called geographical quality and its limitations leads to bottlenecks and incomprehension. This is the reason why Kadaster has started a program, the Cadastral Map Next program, aiming at the development of a methodology for the development of a new version of the cadastral map. The aim of this new version is that the location of boundaries is so accurate, that the boundary coordinates from the map are usable for a better approximation of the boundary location in the field and can accommodate future demands and developments. This development process is based on the use of the original field observations. For this purpose, almost all observations on all (historical) field sketches must be processed. There are about 5 million digitally archived field sketches. This is an enormous challenge that requires far reaching automation. The program has investigated whether it is possible to automatically extract the original (mostly handwritten) measurements from the field sketches and to combine this information and re-determine the location of the boundaries with a very high accuracy of boundary points. With the support of several companies, it has been possible to build a cadastral map with a known geometrical quality and verified accuracy. This accurate cadastral map is called ‘Reconstruction Map’, a working title for the cadastral map with known geometrical quality and higher accuracy. Once this map is ready and the involved parties agree, it will be introduced and presented as the ‘Cadastral Map Next’ and replace the current cadastral map. An important step in this process is to redesign the current data model from parcel level to the more specific boundary level to achieve an unambiguous connection between cadastral objects and its related survey data. A challenge in this process is that the current survey documents only describe changes in a parcel, thus different boundaries of a parcel are related to different survey documents. This challenge should be addressed in the new model. The new data model applies the sub-package ‘Survey and Representation’ of the Land Administration Domain Model (LADM), an ISO standard, for solid solutions in their design process. The basic structure of spatial sources, points, boundaries and parcels, all with their own identification, enables to store relevant data, like coordinates, quality descriptions and metadata, as attributes to these objects. Further new relations can be established while previous ones are maintained. The concept of the ‘Reconstruction Map’ and the ‘information layer’ (metadata) will bring new insights to establish new relations and so relate the different cadastral objects in a more dedicated way.