How to georeference a floor plan: control points, rotation and scale

To georeference a floor plan is to pin it to real-world coordinates, so that every point on the drawing has a latitude and longitude. A floor plan on its own lives in paper or drawing units with its own idea of “up”; once georeferenced, it sits on the map exactly over the building, at the right size and rotation. Spatial Map is a browser-based indoor mapping platform where this is the first step for every floor: you place the plan on a real map and line it up with the building before anything is drawn on it.

Mathematically, georeferencing a clean plan needs four numbers: a shift east–west, a shift north–south, a rotation and a scale. Everything in this guide is about getting those four right, and noticing when a plan needs more than that.

• Outdoor context. Car parks, yards, gates and neighbouring buildings appear around the plan where they really are.
• GPS handover. At an entrance, an outdoor GPS position and the indoor map agree, so a person or vehicle does not jump across the site.
• Positions from other systems. RTLS engines, gateways and vehicle trackers often report latitude and longitude; they only land in the right room if the plan is in the right place.
• Several buildings. On a campus or a logistics park, buildings line up with each other and with the roads between them.
• True measurements. Distances, areas and walking times are right, because the map is in metres, not drawing units.
• Exchange with GIS. Shapes drawn on a georeferenced plan can be compared with site and GIS data without a manual transformation.

GIS tools georeference with control points: pairs of “this point on the drawing is this point on the ground”. The number of pairs decides which transformation you can solve, and the right transformation depends on how clean the plan is.

1. 1
   Pick points far apart

   Opposite corners of the building, not two corners of one wall. Errors in angle shrink with distance.

2. 2
   Pick points you can see on both

   Outer building corners at ground level, column grid intersections, the corners of a stair core.

3. 3
   Use more than the minimum

   With a third or fourth point, the tool can report the leftover error (often as an RMS value). A single point with a large error is usually a misidentified point.

4. 4
   Check a point you did not use

   The far corner of a loading dock or a gate post: if it lines up, the result is good.

Spatial Map does not have a control-point solver. Georeferencing is done directly on the map, which for clean plans amounts to a similarity transformation done by eye — and the scale part is usually already solved by the import.

1. 1
   Fix the scale at import

   A PDF sheet gets its size from its drawing scale or a known width; a DWG from its drawing units. An image gets its real Width (or Height) typed in the panel, with the aspect ratio locked.

2. 2
   Find the building and drop the plan

   Search the address with Search places…, then drag on the map to place the plan. For a scaled PDF or DWG, only the position follows your drag.

3. 3
   Make it see-through

   Lower Opacity so the basemap’s building outline shows through the plan.

4. 4
   Rotate

   Use the Rotation slider (−180° to +180° in 0.5° steps) or [ and ] for 1° (Shift for 15°). Match the longest straight façade first.

5. 5
   Nudge

   Arrow keys move the plan 0.5 m, Shift 5 m. Check the far corner, then the opposite one.

The Position section shows the latitude and longitude of the plan’s centre, which is useful for writing down where a floor sits. Stack further floors at the same spot with their own Elevation, aligning each to the same stair core; hide or fade the others while you work. Every control is in the floor plan tool guide, and the scale side in the PDF and DWG import guide.

Three floors georeferenced to the same building footprint

Once the plan is in place, everything drawn on it — rooms, walls, racks, doors — inherits the georeference, and live positions in latitude and longitude land in the right room. If a newer drawing arrives, Replace image swaps it in at the same position and size. The full path from file to working map is on floor plan to indoor map; Spatial Map’s 7-day free trial covers up to 5 facilities, no card needed.