Application of 3D Cadastres as a Land Policy Tool (Land Lines Article)

Author(s): Erba, Diego Alfonso
Publication Date: April 2012

7 pages; Inventory ID LLA120403; English

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The January 2010 earthquake in Haiti produced an estimated 20 million cubic meters of debris in 35 seconds, even though significant land displacements were not registered. From the point of view of the cadastre, however, these two disasters had very different impacts. If the urban information had been structured in thematic layers and integrated in a GIS platform, the earthquake in Haiti would have affected the construction layer and several representative building types would have disappeared. In Chile, the construction layer was modified mainly by the tsunami, but the land itself was affected by the spatial displacement and shifts resulting from the telluric movement. Fast-moving natural disasters like these change the environment and people's lives radically, and have important implications for government priorities, including definitions and implementation of land policy, both before and after such events.

Predictable climate change events, underground contamination, air pollution, and other such data can be mathematically modeled before they happen. By connecting these models with the spatial databases of a 3D cadastre, it is possible to create prospective 3D scenarios of the potential impacts and identify the neighborhoods and properties that could be affected. Unpredictable phenomena such as earthquakes and sudden flooding can be represented much more quickly if the measurement instruments tracked by environmental institutions or government agencies are connected to the spatial databases of 3D cadastres. The spatial representation of the impact can be made available soon after the event.

In sum, the 3D representation can help define preventive land policies to address predictable changes and also enable the readjustment of current land policies after unpredictable natural events.

3D Networks and Infrastructure
Infrastructure and transport networks move through 3D parcels in different ways and allow the city to remain active and fluid. Some of these networks are invisible by nature, such as the microwaves of cellular phones; others are invisible because they are located underground, such as infrastructure tunnels and pipes; and others are easily visible because they are built on the surface, such as roadways or utility lines. Figure 4 illustrates some of the complex spatial intersections that occur in the overlapping layers of infrastructure and transportation networks within 3D parcels.

These spatial relationships among networks and public and private properties, environmental reserves, mineral deposits, water bodies, and other features have been treated inefficiently through 2D cartographic norms, but they require the development of specific, new 3D norms to enforce the social function of property with equity and justice. For example, Article 1.286 of Brazil's Civil Code states that a landowner is obligated to provide a right of way through her property for cables, pipes, and other underground conduits that serve the public at large and could not be built elsewhere. The law also outlines the need to determine the amount of area affected by public works projects in each parcel and its corresponding value in order to calculate the compensation due to the owner. 3D cadastral records can be an important contribution to facilitating such transactions.

3D Land Market Value
One of the functions of a territorial cadastre is to provide information to determine the value of the parcels with respect to property taxation and urban planning policies. In Latin America, land values generally have been based on ad hoc valuation methods (such as the replacement value of buildings) that use construction data and land values for each cadastre sector (Erba 2008). This practice does not always produce reliable valuations because it is difficult to keep the cadastral databases up-to-date, and the implementation of the valuation methods may be arbitrary from place to place.

An alternative valuation method now being implemented across the region is the use of spatial econometric models to determine property values with the desired level of statistical precision. This is important because land values change across urban space and depend on variables such as urban regulations, environmental restrictions, scenic views, infrastructure, and other features associated with the property, such as underground or airborne elements.

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