Apps that show you where to dig do not exist. Something else does, and it works better: a historical map overlaid on modern satellite imagery, with your GPS position on top.
That's the whole trick. You stand in the middle of a field and the screen shows that a street ran exactly here, and an inn stood over there by the road.
Why it matters
Lost villages and roads. They're absent from modern imagery — ploughed out, built over, forgotten. On 19th-century topographic and military sheets they're still there.
Context for a find. A pin on an 1860s map explains why the signal turned up beside a former inn rather than "just in a field". In a year that will be the only thing you remember.
Planning at home. The polygon gets marked from the sofa, the offline area downloads over wifi, and in the field you no longer depend on whether there's any signal.
What the app has to do
Layer opacity. Without an opacity slider an overlay is useless: you see either the old map or the satellite, never the correspondence between them.
Offline and import. Formats like RMaps and .sqlitedb are widespread among detectorists for a reason — interesting places rarely have coverage. There is a pattern here: the more promising the spot, the fewer bars on the phone. Discovera supports import and offline areas, and the site has free georeferencing and tile-preview tools.
Georeferencing scans. A scan without coordinates is a picture. To become a map it needs control points: in the browser that's the Georeferencer, and the result then opens in the app.
And the thing that shouldn't be there: handing out precise find coordinates. A community map archive is about base layers and local knowledge, not about where to run with a spade.
Choosing
If you just want to look at a historical layer, a focused mapping app with ready-made overlays will do.
If you want the full cycle — maps, pins, a finds catalogue, photo analysis — one app for all of it makes more sense than assembling an outing from four services and your phone's gallery.
And if you've lived in Locus or another navigator for years, nothing stops you keeping it for tracks and adding a separate tool for the journal and the map archive.
Sheet series by region
- Russia and CIS: the imperial topographic surveys and Soviet military sheets cover the 19th–20th centuries.
- Poland: WIG (mapywig.org), 1:100k and 1:25k.
- Germany: Messtischblatt 1:25k, via Deutsche Fotothek and SLUB.
- France: Cassini maps and cadastral plans through Géoportail.
- UK: Ordnance Survey historic sheets — see also reading old maps.
A sheet with no georeference and no offline copy is close to useless in the field, so the pre-trip minimum looks like this:
- Pick a sheet for the region.
- Check the georeference — does the layer drift against satellite?
- Download the offline area.
- Mark where you can't go: private land, protected areas, monuments.
- In the field, keep pins and shoot with context.
How to read the symbols themselves is in reading old maps.
FAQ
Which historical-map app is best?
The one with three things: an overlay with opacity, offline support and honest georeferencing. For the full cycle on Android that's Discovera; for viewing layers, a dedicated mapping app is enough.
Can I use maps without internet?
Yes, if you downloaded the area or imported a tile database beforehand. "Beforehand" being the operative word — discovering there's no signal while standing in the field is too late.
Where do I get and georeference a scan?
Scans come from open archives and legitimate sources. You can georeference in the Georeferencer and open the result in the app.
Is this legal?
Reading historical maps, absolutely. What's prohibited is searching for and removing archaeological objects without authorisation, and working on protected sites. See legal status.
Bottom line
The working combination is simple: a historical overlay, offline coverage and the discipline to keep pins. Everything else is implementation detail. Discovera puts it in one Android app and backs it with browser tools on the site.