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This page gives more in-depth information about the GRB import.

Main issues

The main issues we have had to solve:

  • Conversion to OSM categories: It isn’t always possible to convert the GRB categories to a corresponding OSM tag. But a good effort gets a long way. In case of doubt, we can use building=yes. The import toolset will result in warnings when trying to change existing tags. Because of how we plan to tag, QA tools will be easy to set up, to identify possible tagging mistakes. Several categories of mistakes are already identified and accounted for.
  • Existing buildings: About 1.5 million buildings exist in OSM already. The toolset will respect these objects, and their mappers. The geometry and tags will be changed but the object ID and hence their history will remain.
  • Address data: Complex addresses are flattened onto buildings in GRB. These addresses will not be imported. Instead, they can be sourced directly from CRAB, helped by local surveys.
  • Complexity of the mapper's job: To assure quality importing, the tool will be properly documented, there will be workshops and hangouts. Only people who had some training will be allowed to import into OSM with the toolset. However, we have to be careful not to be off-putting: people are already deleting-and-tracing from GRB background images or doing wild imports. The toolset will definitely improve current mapping practices.
  • Updating: Our community has the skills to keep using the GRB to detect errors once a larger amount of GRB buildings are imported. In many cases, we will be faster than the GRB, in many others we will be slower. Marc Ducobu has done a presentation at SotM about the exact same problem in Brussels, where a building import happened a lot earlier, using UrbIS data. These tools will serve as inspiration or will be extended to cover Flanders.


The Large scale Reference Database (Grootschalig ReferentieBestand) of Flanders is produced by AIV and is the data source for building outlines in this import. The English initialism is LRD.

This detailed database focuses on government operated infrastructure on the public domain. It contains amongst others building footprints, both road axes and road surface area outlines, roadside infrastructure, administrative parcels and water bodies. Most publicly accessible features (e.g. the front sides of the buildings) have been measured on the ground with great accuracy (typically better than 10 cm).

A detailed analysis of GRB entities and their possible translation to OSM objects is available at the WikiProject Belgium/GRB page.

Their main focus is accuracy, not recency. Changes are only made if an as-built plan is received, or when surveyors have been on the ground. Any change on the ground should become available within a year on a worst case basis. [link: details of update procedure]

Only data that can be collected from public land is measured, so the backside of buildings is drawn based on high resolution imagery. The building dataset contains addresses, which are periodically updated from the central address database (CRAB).

In the period 2000–2013, the GRB was established for all Flemish cities and municipalities. This detailed database focuses on government operated infrastructure on the public domain. It contains amongst others building footprints, road morphology, road infrastructure and administrative parcels. Everything that is accessible or visible from the public domain was collected by professional surveyors to within 25 cm accuracy. Everything in the public domain is checked for updates at least once a year. Since the original creation of these databases, no updates were executed at the level of the inner terrains (areas not accessible for surveyors). In 2013 an update was executed based upon terrain changes (anomalies), midscale aerial imagery on more than 5.500 km² were screened for changes at the level of the inner terrains. In total, more than 400.000 anomalies were checked and updated by means of photogrammetric mapping on the midscale imagery.

In December 2015, the data was made publicly available but registration was required. The database is maintained and updated by Flemish municipalities using administrative procedures, geodesy measurements and satellite photos. It forms the geographical basis which others can use to inoculate their data. The Flemish government expects a positive effect on the quality of the data through feedback channels. Furthermore, it expects the development of new data sets and the creation of GRB data-based applications.


The Central Reference Address File (Centraal ReferentieAdressenBestand) is AIV's database with addresses and their positions. The import procedure for this database was started but it has stalled now that we're planning to import the building outlines. The CRAB's addresses are copied to GRB almost manually, so they are more up-to-date and correct. Importers use CRAB to do a check-up round after GRB's buildings are added.


The Agency for Information Flanders (Agentschap Informatie Vlaanderen or Informatie Vlaanderen) is the Flemish governmental agency tasked with producing geo information and digital data.

AGIV (Agency for Geographic Information Flanders, Agentschap voor Geografische Informatie Vlaanderen) is the name of the old and abolished agency tasked with geo data. It merged with some other entities to form AIV. The name is deprecated but is still in wide use, even on portals of the agency itself and in data attribution requirements.


UrbIS is the Urban Information System of the Brussels region. Buildings from there are imported independently from this import.