Old paper maps hold information that no modern dataset can replace: field boundaries from decades ago, historical street layouts, and survey notes made before digital mapping existed. To use one in a modern mapping project, it first has to be georeferenced, which means tying points on the scanned image to real-world coordinates so the map sits in the right place on the Earth. QGIS, the free and open-source mapping program, includes a built-in Georeferencer tool that makes this possible without any paid software.

Georeferencing sounds technical, but the idea is simple. A scanned map is just a picture made of pixels. It has no idea where on the planet it belongs. By clicking on a few features that you can identify on both the scanned map and a modern reference map, such as road intersections or river bends, you teach QGIS how to stretch and place the image so it lines up with reality. Four or more well-spread points will usually give a usable result.

Start with the best scan you can get. Scan at 300 dots per inch or higher, keep the page as flat as possible, and save the result as a TIFF or PNG file. Crooked pages and folds create distortions that no amount of control points can fully fix, so if the map is large, scan it in sections and work with the cleanest copy. Note anything printed on the map that helps later, such as a scale bar, a north arrow, or a grid with coordinate labels.

Open QGIS and create a new project. Before you load the scan, add a modern reference layer so you have something to compare against, such as an OpenStreetMap basemap. Set your project coordinate system to a common one like WGS 84, unless you already know the original map used a specific local projection. If the map has a printed grid, the coordinate values on its edges will tell you which system it used, and matching that system will improve your accuracy.

Open the Georeferencer from the Raster menu and load your scanned image. You will see it in a separate window. Click the Add Point tool, then click a feature you can identify clearly, such as the corner of a building, a bridge, or the intersection of two roads. A dialog will ask for the coordinates of that point. The easiest way to fill it in is to click From Map Canvas, which lets you click the same feature on your reference map and copies its coordinates automatically.

Repeat this for at least four points, and spread them across the whole map rather than clustering them in one corner. Corners and edges matter: points near all four sides of the image anchor it far better than a tight group in the middle. Choose features that have not moved over time. A road junction that still exists is a good choice, while a shoreline or a riverbank that may have shifted is less reliable. After each point, check the residual error shown in the table, which tells you how far off that point sits. A point with a much larger error than the rest is worth re-checking, since it may have been clicked in the wrong place.

When your points are placed, open the Transformation Settings. For a first attempt with a flat, undistorted scan, the Linear or Helmert transformation is a good choice, since it only shifts, rotates, and scales the image. If the scan is a photograph of a page with visible curvature, or an old map that was never drawn to a consistent scale, Thin Plate Spline will bend the image to fit your points more closely, though it can also distort areas far from any control point.

Set the resampling method to Cubic or Nearest Neighbour, choose an output file name ending in .tif, and tick the boxes to save your ground control points and load the result into QGIS when done. Saving the points matters: if you later spot an error, you can reload them and adjust a single point instead of starting over. Click Start Georeferencing and wait for the process to finish.

Once the georeferenced map loads into your project, compare it against the reference layer. Do roads line up, and do rivers follow the same courses? Zoom in at several locations, not just the centre. If one area is off while the rest is fine, add another control point there and run the process again. If the whole map is rotated or shifted, one of your points was probably entered with swapped coordinates, a common mistake where longitude and latitude are entered in the wrong order.

Keep the original scan, the saved control points file, and the georeferenced output together in one project folder, and write a short note about the source of the map and the date you georeferenced it. That record makes your work reusable, and it is what turns a one-off experiment into a dataset other people can trust. With practice, a straightforward map takes well under an hour from scan to a finished, correctly placed layer.