Mapper — charts on a relief map

This is a figure composer, not an analysis. You place pie and donut charts, keys, labels and images onto a shaded-relief basemap, position them over the places they describe, and export the result as a high-resolution image or an animated MP4. It is the step between having numbers and having something a reader can follow — the same job the map figures in an ancient-DNA paper do.

Charts anchor to the map rather than to the screen, so a chart placed over a region stays over that region when the view moves or the export renders at a different size. That is what keeps the exported figure saying the same thing as the one you composed; a chart pinned to screen coordinates drifts off its location the moment the canvas dimensions change. Everything runs in your browser and your composition is saved locally, so work in progress stays on your machine.

The honest caveat about map figures: placing a pie chart on a country is a claim about where a population was, and the map makes that claim look more precise than the underlying data usually is. Ancient samples come from specific sites, not from territories, and modern labels rarely match ancient boundaries. Label what a chart represents and over what period, and prefer putting a chart near the sites the samples came from rather than at the centre of a modern country.

The standard job: turn an admixture breakdown into a publishable map figure. Start from the numbers — a fit from the admixture calculator, or any percentages you can defend — and place one donut per population near the sites its samples came from, not at a capital city. Add a key listing the source panel, one label stating the era, and scale the charts so the smallest slice worth mentioning stays legible at the export size. Because charts anchor to the map, the composition survives panning, zooming and export resolution unchanged — the figure you export says what the figure you composed said.

For the moving version, the MP4 export animates the composition — the same anchoring rules apply, and the usual use is a slow pan across a labelled region for posts and presentations. Compositions save locally in your browser, so a figure can be refined across sessions without an account and without anything leaving your machine.

The discipline that separates a good figure from a misleading one is inherited from the caveat above: every chart is a claim about place and period, and the map lends it false precision for free. The cure is labelling — what the percentages are, against which panel, for which era — because a reader who cannot see the model behind a chart can only over-read it.

The hobby's usual figure pipeline is a screenshot into a slide deck or image editor: quick, and permanently fragile — charts pinned to screen pixels drift off their locations at every crop, and the basemap arrives at whatever resolution the screenshot happened to capture. At the other extreme sits real GIS software (QGIS and kin), which does everything this tool does and far more, at the cost of a genuine learning curve and manual chart-building. There is no established free middle ground for exactly this job — ancestry charts, anchored on a relief map, exported at figure quality — which is the niche this composer fills.

What it deliberately is not: an analysis, a data source, or a claim-checker. It renders whatever numbers you bring, wrong ones included, and no styling improves a model the arithmetic upstream cannot defend. Bring numbers from tools that state their panels and fits — then make the figure worthy of them.