Building Changes · Leuven

The GRB (Grootschalig Referentiebestand) is Flanders' large-scale reference map, and its GBG layer holds every building footprint on the ground. Each building carries a stable identifier (OIDN) and a version identifier (UIDN) that changes whenever the object is edited, so consecutive snapshots can be compared building by building.
This page compares seven snapshots of Leuven, two years apart from October 2014 to October 2026, and separates real changes to buildings from the much larger stream of data corrections — see the for the rules, and click a footprint for its details.

Real building changes 2014 → 2026

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Zoom in for individual changes, coloured by class.

What's on the map

Two layers built from seven GRB snapshots by a Node script at build time (no GIS stack needed: it reads the GeoParquet snapshots, compares footprints and reprojects Lambert 72 to WGS84 itself), rendered client-side on the same MapLibre GL map and Protomaps basemap as the high-voltage page.

Change density heatmap

One point per building event in the selected period, weighted equally and blended into a density surface. Zoomed in past street level, the surface gives way to the individual events, coloured by class.

Before / after footprints polygons

For every real change, the footprint after the change (filled) and before it (dashed). About 24 000 outlines; they load the first time the Changed buildings tab is opened.

Correction density heatmap

The same density surface for data-only edits, in the cooler palette. In 2014–16 it lights up almost the whole city: that is the alignment of the GRB with the cadastral parcel plan (kadastralisatie).

Selected row dynamic

Clicking a row in a table flies the map to that cell or building and marks it with a pulsing halo; on the buildings view the matching footprints get a white outline. Click empty space on the map to clear it.

How changes are detected

Each pair of consecutive snapshots is compared building by building:

Same building, new version OIDN kept

When the UIDN changed, the old and new outlines are compared: overlap (IoU, sampled on a fine grid), the largest outline shift (Hausdorff distance) and the area change decide between outline correction, extended, reduced, reshaped and rebuilt. Unchanged geometry with a new label counts as an attribute-only edit.

Buildings that disappear or appear new OIDN

Overlapping disappeared and new footprints are grouped and judged together. If the group's old and new footprints match, it is a split, merge or redrawn outline (a correction); otherwise it is a rebuild, extension or reduction on the same site. Footprints with nothing on the other side are new or demolished.

GRB process labels LBLBGNINV

Edits carried by kadastralisatie, tertiaire kadastralisatie, aanmaak uniek percelenplan or correcties always count as corrections. Maintenance updates and dataset-ingestion operations (adpupdate, lokale bijhouding adp, globale bijhouding) say nothing about the building itself, so the geometry decides.