Map Extract — Georeferencing

Select PDF

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📘 Instructions ▼

1️⃣ Upload your map
Click “Select PDF”.

2️⃣ Add GCPs
Toggle Georeference Mode, then click points on the map.

3️⃣ Enter lat/lon
Fill in longitude/latitude for each GCP in the table.

4️⃣ Compute transform
Click Compute Transform to calculate an Affine transform.

5️⃣ Review accuracy
Check RMS error and per-point errors in the table.

Ground Control Points

RMS error: —

...

Transform Model: Affine

Overlay controls

Basemap opacity

Uploaded map opacity

Georeferencing method: This site uses an Affine transform. Affine is a stable, industry-standard approach that corrects global shift, rotation, scale, and skew without “bending” the map. A 2nd-degree polynomial transform can warp the image to fit local distortions (like folds or stretching), but it can also introduce unwanted bending and distort shapes or distances. For most scanned maps (about 90% of cases), Affine is the safest and most predictable choice.