romanroads

Visualiser for the RRRA's Roman road dataset.

An unofficial web map viewer for Digital Britannia v1 from the Roman Roads Research Association. It shows the dataset's engineered Roman roads, forts, temporary camps, settlements, milestones and Hadrian's / Antonine Wall features over LiDAR hillshade, historic OS maps and aerial imagery.

Data: Digital Britannia v1, © Roman Roads Research Association / Mike Haken. CC BY-NC 4.0, non-commercial use only. This viewer is not endorsed by the RRRA.

View the map

Online

The map is live at https://adrianco.github.io/romanroads/, served by GitHub Pages from the docs/ folder of main. Each push to main redeploys it within a minute or two.

Locally

The viewer fetches its GeoJSON over HTTP, so opening docs/index.html straight from disk (file://) won't work. Serve the docs/ folder instead:

python3 -m http.server 8765 --directory docs

Then open http://localhost:8765.

Using the viewer

• Search (top of the panel): a modern place name (Housesteads), a Roman name (Vercovicium) or a road number (RR2, 2a). Road results zoom to the whole route.
• Click any road or site for a popup with every attribute and clickable links. Clicking a road highlights its entire Margary route in blue.
• Underlays: tick LiDAR hillshade, historic OS maps (choose the edition), aerial imagery, the Roman Empire map or geology, and set each one's opacity with its slider. Untick Show roads to look at the bare terrain. Tick 3D terrain to show its sliders: Tilt (0–85°), Rotation, Altitude (zoom) and Relief (vertical exaggeration, 1–5×). The sliders follow the map as you move it, and turning 3D off returns to a flat, north-up view.
• Heritage overlays: scheduled monuments and Roman-period aerial mapping load for the area in view once you zoom in. The line under each one says how many features are showing.
• Period slider: shows only military sites occupied in the chosen period, coloured by their type in that period.
• The URL keeps the current view (#zoom/lat/lon), so you can share a link to a specific spot.

What was built, and how

1. Data processing (scripts/process.py). The GeoPackage's layers are reprojected from British National Grid (EPSG:27700) to WGS84 (EPSG:4326) and written as one GeoJSON file per layer.
   • No simplification. Every original vertex is kept; coordinates are only rounded to 7 decimal places (~1 cm). Road positions carry stated accuracies of ±30 m and ±200 m, and simplifying would degrade them.
   • Cleanup of the source's inconsistent values: category spellings (Legionary Fortress / Legionary fortress), one garbled settlement type, NULL text glued onto values (which broke some links), and padding whitespace. The GeoPackage itself is never modified.
   • The empty Hadrians Wall Turrets layer is skipped.
2. Symbology follows the author's own QGIS styles, read from the GeoPackage's layer_styles table. Roads are solid / dashed / dotted by confidence; sites are coloured by type, as in the author's project.
3. Viewer (docs/index.html). A single page using MapLibre GL JS, with no build step and no API keys. The full-fidelity data is 4.19 MiB in total, under the 5 MB budget for a single page, so no vector-tile pipeline was needed.
4. Underlays. Each service was checked before it was wired in: its URL, whether it returns real tiles (one base-map provider returned "API KEY REQUIRED" watermarks and was dropped), its coverage, and its licence.
5. Errata (docs/ERRATA.md). Every data issue found along the way, with counts and examples, written up for the RRRA's next release.
6. Decisions are recorded as ADRs in docs/adr/.

Features

• Roads styled by Segment Confidence: solid = certain ±30 m, dashed = probable ±200 m, dotted = conjectured. "No evidence" segments are hidden by default. Margary RR number labels. Roads get a white halo so they stay readable over the underlays.
• Sites symbolised by type, with a toggle for "possible" sites.
• Period slider using the per-period type fields (Claudio-Neronian … 4th century).
• Underlays, each with an opacity slider:
  • LiDAR hillshade:
    • England: Environment Agency 1 m composite.
    • Scotland (from zoom 11): DTMs from the Scottish Remote Sensing Portal, shaded on the fly by its server.
    • Wales: not yet. The Welsh hillshades aren't available in any form a web page can use (ADR 0006).
  • Historic OS maps: National Library of Scotland, 6-inch 2nd edition (GB) and other editions
  • Aerial imagery: Esri World Imagery
  • Roman Empire map: the Digital Atlas of the Roman Empire (DARE), with Latin place names
  • Bedrock geology: BGS, 1:625k zoomed out and 1:50k zoomed in
  • 3D terrain: tilts the view with real elevation
• Heritage overlays:
  • Scheduled monuments for England (Historic England), Scotland (HES) and Wales (Cadw).
  • Historic England's aerial mapping of Roman-period features (England, from zoom 14): cropmark and earthwork ditches, banks and structures.
• Itiner-e comparison: tick Compare: Itiner-e roads to draw the Itiner-e 2024 network for Britain in magenta, under the RRRA roads, to see where the two datasets agree and differ. Dashed means hypothetical. It's fetched only when switched on. The British Itiner-e segments are stored ~100 m out of place (OSGB36 lat/lon labelled as WGS84), so the viewer corrects them; see ADR 0013.
• Pleiades links: 533 forts and settlements link straight to their Pleiades place, matched at build time by Roman name, or by modern name where there's no Roman one, within 2 km (ADR 0014). The rest fall back to a Pleiades search for the modern name; they're listed in for review. Roman names display in title case ( → "Vercovicium"). Search accepts the modern spelling and Pleiades' standard name ( finds Dorchester's ).

Why each source was chosen, and why others were rejected, is in ADR 0012.

Layout

data/digital-britannia_v1.gpkg   source GeoPackage (EPSG:27700)
scripts/process.py               GeoPackage -> per-layer GeoJSON (EPSG:4326)
requirements.txt                 pinned Python dependencies
docs/index.html                  the viewer (single page, MapLibre GL JS)
docs/data/*.geojson              processed layers + manifest.json (itinere.geojson = Britain subset)
data/external/                   third-party downloads (gitignored)
docs/ERRATA.md                   data issues to report back to the RRRA
docs/adr/                        architecture decision records

Rebuild the data

python3 -m venv .venv
.venv/bin/pip install -r requirements.txt
.venv/bin/python scripts/process.py

The Itiner-e comparison layer comes from a 33.6 MB empire-wide file that isn't committed. Only the Britain subset (docs/data/itinere.geojson) is. To rebuild it, download itinere_roads.gpkg from Zenodo record 17122148 into data/external/ (gitignored) and rerun the script. Without the file, the script keeps the committed subset.

Pleiades matching works the same way. Download pleiades-places-latest.csv.gz and pleiades-names-latest.csv.gz from the Pleiades dumps into data/external/pleiades/, and the script re-matches and rewrites data/pleiades_matches.csv and data/unmatched_pleiades.csv. Without them, it reuses the committed match table.

How

A blog post records the development process over two days. Dev.to blog

Credits

• Data: Digital Britannia v1 © Roman Roads Research Association / Mike Haken (CC BY-NC 4.0)
• LiDAR (England): contains Environment Agency information © Environment Agency and/or database right
• LiDAR (Scotland): © Crown copyright Scottish Government, SEPA, Fugro, Historic Environment Scotland and partners, via the Scottish Remote Sensing Portal (OGL)
• Historic maps: National Library of Scotland
• Roman Empire map: Digital Atlas of the Roman Empire, Johan Åhlfeldt (CC BY 4.0)
• Places: Pleiades, Copyright © The Contributors (CC BY 3.0), https://pleiades.stoa.org
• Comparison roads: Itiner-e static version 2024, Brughmans, de Soto, Pažout & Bjerregaard Vahlstrup (CC BY 4.0), https://doi.org/10.5281/zenodo.17122148
• Geology: contains British Geological Survey materials © UKRI
• Heritage (England): © Historic England, contains OS data © Crown copyright (OGL)
• Scheduled monuments (Scotland): © Historic Environment Scotland, Scottish Charity No. SC045925, © Crown copyright (OGL)
• Scheduled monuments (Wales): Cadw, via DataMapWales (OGL)
• Terrain: Mapzen terrain tiles on AWS Open Data; UK terrain data © Environment Agency 2015; EU-DEM (Copernicus); SRTM/GMTED2010 (USGS)
• Imagery and base maps: © Esri, Maxar, Earthstar Geographics, HERE, Garmin, and the GIS User Community
• Base map: © OpenStreetMap contributors