Load your map
JPEG, PNG, WebP or IIIF. Multiple sheets can live in one project.
BROWSER-BASED MAP GEOREFERENCING
Overlay historical maps.
See what changed.
GeoCalque lets you compare maps directly, or georeference a scanned historical map against a modern reference using ground control points (GCPs).
Local rasters stay in your browser by defaultAffine · Projective · Thin Plate SplineDesktop & mobile
FAST WORKFLOW
From scan to georeferenced overlay in a few steps.
Load a raster or IIIF resource, add control points if needed, choose a transformation and inspect the result on a reference basemap.
Add ground control points
Click matching features on the historical raster and the reference map. GeoCalque reports residuals and RMS error.
Inspect the overlay
Use opacity or swipe, switch basemaps, clip scan margins and apply a reversible visual offset when needed.
TWO WORKFLOWS
Quick visual comparison or proper georeferencing.
Quick comparison
Compare two local rasters, or two already-georeferenced basemaps, with synchronized navigation, opacity and swipe.
No GCPs requiredGeoreferencing
Use ground control points and choose an affine, projective or Thin Plate Spline transformation. Inspect point residuals and RMS error before trusting the overlay.
GIS-oriented workflowGlobal + France-specific basemaps
OpenStreetMap and OpenTopoMap are available globally. In France, IGN aerial imagery, cadastral parcels, historical layers and experimental GeoCalque access to LiDAR HD DTM/DSM/height hillshades are available where coverage exists.
Portable projects
Export a complete .geocalque project with its images, control points, clipping masks and settings, or optionally save it to your private cloud account.
Already have a historical map?
Start without an account. Files loaded from your device stay in browser storage unless you explicitly use cloud save.