Georeferencing a scanned map online means aligning it with real-world coordinates. You do this by picking control points—matching features on your scan to a modern map. In Gratic, this is the first step in a continuous workflow: align your old map, then immediately trace over it with professional cartography tools to create a new vector map. The entire process, from uploading your scan to creating a file for OCAD, happens in a single browser tab.
The real goal of georeferencing a map
The real goal of georeferencing is to turn a static, scanned image into a useful, positioned reference for creating a new map. It’s not just about making a picture line up on a screen. The process corrects for the distortions inherent in old paper maps—the shrinkage from humidity, the wear along folds, the inaccuracies of past survey methods, and sometimes even the projection itself. When I built the georeferencer for Gratic, I was thinking about the problems I’ve had with old forest maps, where the north edge might have stretched differently than the south.
To do this, you need to establish control points. These are identifiable locations that appear on both your scanned map and a reliable modern base map, like the satellite imagery or road data we load into Gratic. A sharp road intersection, a building corner, a stream junction—these are good candidates. You click the point on your scan, then click the corresponding point on the base map. With each pair of points, the software calculates the transformation needed to stretch, scale, and rotate your image into place. The more points you add, distributed across the map, the more accurate the fit becomes.
The output of this process isn't the final product; it's the starting block. The georeferenced image becomes a template, a ghost layer that guides your hand as you draw the new vector features. Its purpose is to be traced over, corrected, and ultimately superseded by the clean, accurate data of the new map you are creating. It’s a bridge from the past to the present state of your terrain.
Choosing an online georeferencing tool
You should choose a tool based on whether you need a one-off rectified image or an integrated step in a larger map-making project. Different tools are built with different end goals in mind, which determines their place in your workflow. Your choice depends entirely on what you plan to do after the map is aligned.
For instance, a well-known open-source tool is Map Warper. It is excellent for its specific, dedicated purpose: to georeference a scanned map and make that aligned image available, often for historical or archival projects. It does this one job very well. If your goal is simply to have a correctly positioned image to look at or share, it's a solid choice.
I built Gratic with a different assumption. I believe that for a cartographer, georeferencing is rarely the final step. It's step one. The real work—the drawing, editing, and symbolizing of a new map—begins immediately after. I found that exporting a georeferenced image from one tool and importing it into a separate drawing program was an unnecessary interruption. It adds a file-management step that breaks the flow of work.
That’s why in Gratic, georeferencing is not a separate function but part of a continuous sequence. You upload your scan, align it using control points against the base data, and the moment you are done, it becomes a template layer in the editor. You can immediately select a pen and start tracing a path or a fence using the correct ISOM symbols. There is no export/import cycle. The focus remains on the cartography, not the software juggling.
The full workflow in Gratic
A full workflow in Gratic takes you from a blank screen to a finished vector map file without changing applications. The process is designed to get you from raw data to a usable orienteering map as directly as possible, keeping all your sources in one context.
It starts when you open a browser tab and load Gratic. You find your project area on the world map and draw a rectangle. Gratic then automatically pulls in the data we have for that location. This includes elevation data, which we use to draw contour lines for you, and any vector data we can source from national mapping services—roads, buildings, water features. This gives you an immediate, workable base map.
Next, you upload your scanned map. This could be an older version of an orienteering map, an aerial photograph, or a historical survey sheet. The georeferencing tool opens, placing your scan alongside the base map. You pick your control points, clicking on a feature on your scan and then on the same feature on the base map. Once you have enough points for a good fit, you apply the transformation.
Your scanned map now appears as a semi-transparent layer, perfectly aligned with the contours and vector data. From here, the drawing begins. You can select from standard symbol sets and use pens designed to behave as a cartographer expects. You trace features from the old map, correct them against the new data, and add details from your own field survey.
Each object you draw is a clean vector element on its own layer. When you are finished, you save your work. The output is a file that opens directly in OCAD, ready for final layout and printing.
The benefits of an integrated workflow for making terrain maps
An integrated workflow is better because it saves time and reduces the friction of moving files between different, single-purpose programs. Every time you have to export a file from one tool and import it into another, you introduce the possibility of conversion errors, projection mismatches, and data loss. More importantly, you break your concentration. The task becomes about file management instead of cartography.
A mapper creating a terrain map for orienteering is fundamentally a synthesizer of information. You are combining data from multiple sources: an old map for historical context, satellite imagery for vegetation, official data for roads and buildings, and your own GPS tracks or field notes for the fine details. I wanted Gratic to be the single place where all that information comes together coherently.
By building the georeferencer directly into the editor, the scanned map becomes just another piece of data you can toggle on and off. You can compare a trail on the old map against the contour lines we generated and the tree lines visible on the satellite layer. Is the path still there? Has it moved?
Does it follow the terrain logically? You can make these judgments instantly because all the evidence is in one place. This allows you to focus on the real work: making informed decisions to draw the most accurate map possible.