Cadastral mapping for underground networks: A preliminary analysis of user needs
ISBN 978-85-88783-11-9
Authors
1Pouliot, J.; 2Cuissart, R.; 3Bordin, P.
1UNIVERSITÉ LAVAL Email: jacynthe.pouliot@scg.ulaval.ca
2ECOLE NATIONALE DES SCIENGES GÉOGRAPHIQUES
3GEOSPECTIVE
Abstract
Real estate transactions, consisting of the transfer of a unit of property between two or more parties, are common processes, crucial for a healthy economy in land and property markets. For example, in 2011 more than 247,900 real estate transactions were recorded in the Registre Foncier du Québec (Land Register) for an economic value of approximatively C$80 billion (Foncier Quebec, 2011). In Quebec, notaries are required to authorize real estate transactions by providing their professional opinion about the Rights, Responsibilities and Restrictions (RRR) that may affect legal objects. If they express an incorrect judgment, the impact may be critical for the owner (mortgage denied, ownership right disregarded). To support this process, notaries can usually count on cadastral plans, i.e., 2D maps of the land parcel (except for stratified ownership, or condominium, for which a vertical profile is provided). Surprisingly, when legal objects are underground, e.g., utility networks, no cadastral representation (even in 2D) or other data on land parcel restrictions are available to support the decision making process. In this context, this study explores the advantages of accessing (2D or 3D) spatial representation of underground objects to support queries and verification of real estate transactions. To limit the study, only communication networks are investigated and the targeted end-users are notaries, working for government authorities. The study started with meetings with end-users and the investigation of current practices. Based on several case studies, we used reverse engineering to establish conceptual data modelling and three use cases were investigated (1- Find a specific underground legal object, 2- Locate a specific underground legal object, 3- Comprehend the spatial relationship of a specific underground legal object with its surroundings). For communication networks, the required information in the registration process is the name of the network holder and the name of the regional administration. A sequential number is also added for recording in the land file. The title linked to the Land Register may also contain various textual data, including road names, address, description of the surrounding space, etc. In order to demonstrate the advantages of using spatial representation, we propose four analysis axes that may be of interest to end-users (each time the user has to decide if they integrate or not this concept). Axis 1 – Spatial characteristics of the data network: relative or absolute coordinates, a unique identifier, descriptive data, uniform data structure. Axis 2 – Data Network Reliability: existing geometric data or new collected data, internal or external to the current Land Register. Axis 3 – Level of details for spatial representation: dimension of the representation space (2D or 3D), dimension of the objects (0D, 1D, 2D, 3D), annotation, database data. Axis 4- Contextual data: land parcel limits, orthophoto, topographic elements, administrative limits, point of interest, road network, etc. Based on this analysis framework, nine possible map layouts were designed and presented to end-users (for example, one keeps the number of collected data as low as possible, one matches the current vertical cadastre specifications, one is a full 3D model). The final solution selected by the end-users is a 2D map with the absolute coordinates of the maximum extent of a linear (1D) geometric primitive of the network, including a unique identifier, the diameter of the communication cable, with contextual data that shows parcel and administrative limits, street name, and an orthophoto as background. This presentation will discuss the pros and cons of the methodology used, the scenarios investigated and the final solution selected. The results and subsequent discussion may be seen as a first attempt to quantify user requirements for the spatial representation of underground legal objects.