G GeoCalque My map project No area selected
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Start on the left: click a precise control point on the historical map.
SOURCE RASTER

Add a sheet

Select a sheet in the left panel.
⌑

No sheets active

Add a historical raster, then click matching ground control points on the raster and reference map.

Step 1: click a precise corner, road intersection, bridge or other stable feature that is easy to identify on the reference map.
REFERENCE MAP

Reference map / basemap

Step 2: click the exact same feature. For buildings, a mapped footprint is usually more reliable than a roof corner visible in aerial imagery.
GCPs0
Erreur RMS—
Fit quality—
StatusAdd a sheet pour commencer.
Technical fit indicator only · no legal or cadastral-survey value.

Ground control points

Affine: robust and suitable for most maps. Distribute GCPs across the whole raster.

#NomHistorical mapReference mapResidual
No GCPs.
Overlay options
67 %
Choose two local rasters or two basemaps.
Drag the overlay raster with a mouse or finger. Mouse wheel and pinch gestures adjust its scale.
Georeference at least one sheet to display it here.
✓ Project automatically saved on this device
PROJECT

Project summary

AREA

Locate project

Choose a French municipality or use your location to center the maps.

SHEETS

0 sheets

Each sheet keeps its own georeferencing. Multiple sheets can be displayed together in Overlay.

SAVE & TRANSFER

Save and transfer

The project is saved automatically on this device. A .geocalque file also contains the images and can be moved to another computer. Cloud storage remains optional.

My cloud projects
GEOCALQUE

Help & privacy

GeoCalque is independent from archive institutions and mapping agencies. Local files remain in this browser by default.

Privacy Legal notice
INFORMATION

Information
NEW PROJECT

Create a project

1 Area
2 Maps
3 Compare

Search a French municipality

For France, selecting a municipality centers the map and suggests the relevant archive department. It is optional if you only want to compare maps.

or

Your browser asks for location permission. It is used to identify the area; the precise GPS position is not stored.

Already have your map sheets?

You can load multiple scans, georeference them independently, then display them together.

Area: not set · Sheets: 0
ADD SHEETS

Local file or IIIF

↥

From your device

JPEG, PNG or WebP. Images stay in the browser and are not uploaded to the server.

Ⅱ

From an IIIF service

Collez l’URL d’un manifeste IIIF Presentation 2/3, d’un info.json ou de la racine d’un service Image API.

Only HTTP/HTTPS URLs are accepted. Direct import requires the source server to allow browser access (CORS).
FRENCH ARCHIVES GUIDE

Where can I find a high-resolution historical map in France?

Practical rule: do not use “right-click → save image” in an archive viewer unless the site explicitly states that it is the original file. Look for the original download or an IIIF link.
QUICK GUIDE

GeoCalque in a few minutes

1

Locate

Choose a French municipality or use your location to center the map.

2

Add one or more sheets

Each scan or IIIF image is an independent sheet. You can display them together in Overlay.

3

Add control points

Click a precise ground control point (GCP) on the historical map, then the same point on the reference map. Use 6–15 well-distributed GCPs.

4

Compare

After georeferencing, open Overlay. To compare without georeferencing, use Quick comparison.

Which transformation should I use?

Affine — default choice: translation, rotation, scale and shear. Minimum 3 GCPs.

Projective — useful when the raster was photographed or scanned with perspective distortion. Minimum 4 GCPs.

Thin Plate Spline (TPS) — applies a smooth local warp to absorb paper or survey distortion. Prefer 6 or more well-distributed GCPs.

Choosing control points

Church/building footprint corners, bridges, road intersections, wall corners and hydraulic structures are good candidates. For buildings, target the emprise au sol cadastrale rather than a roof corner in aerial imagery.

Avoid agricultural boundaries that may have changed, and avoid clustering all GCPs in one small area.

No georeferencing needed? Use Quick comparison. You can compare two local rasters or two already-georeferenced basemaps, including several IGN historical aerial-imagery periods.

IGN historical aerial imagery: 1950–1965, 1965–1980, 2000–2005, 2011–2015 and 2016–2020 are distributed by IGN through Géoplateforme and offered by Remonter le Temps. The 1965–1980 coverage is still being progressively completed. Source attribution remains discreetly visible on the map.

IGN LiDAR HD: DTM, DSM and height-model hillshades are available in the basemap selectors and in Quick Comparison. DTM represents ground terrain, DSM includes above-ground features, and the height model represents relative heights. Coverage may still be incomplete.

Problem or idea? Contact GeoCalque
OUTILS GIS

Interopérabilité & diagnostic

Affichage cartographique

Une flèche relie chaque GCP à la position prédite par la transformation. Les vecteurs sont amplifiés à l’écran pour rester visibles ; la valeur en mètres reste la valeur réelle.

Ground Control Points (GCP)

Échangez les points de contrôle avec un SIG ou un autre projet.

World file · affine

Import/export en EPSG:3857. L’export produit un fichier .wld et un .prj.

Share & export view

Share the position, zoom and public basemap choices, or export the visible map as PNG when tile providers allow it.
SOURCES CARTOGRAPHIQUES

XYZ · WMS · WMTS

Sources personnelles enregistrées uniquement dans ce navigateur. Les clés placées dans une URL ne sont pas incluses dans les exports de projet.

XYZ : utilisez {z}, {x}, {y}. WMTS : les formes {TileMatrix}, {TileCol}, {TileRow} sont aussi acceptées pour les services Web Mercator.
RASTER PREPARATION

Clipping mask

GeoCalque analyzes the scan from its edges and proposes an irregular clipping mask around useful map content. Text, marginalia and cartouches may require manual correction. The source image is never modified.

The shaded area will be hidden in Overlay.

Sheet
EXPORT

Exporter une image

L’export produit uniquement la carte visible, sans les panneaux ni les boutons de l’interface.
LIDAR HD

Elevation profile

Profile calculated from the line drawn on the map. IGN / Géoplateforme.