How Roman is your road? Data and code

How much of Britain's modern A-road network still follows a Roman line? This record holds the data and code behind the data post How Roman is your road?, which lays the Itiner-e atlas of Roman roads (static version 2024) over every A-road in Great Britain in OpenStreetMap and measures, county by county, the share of A-road length that runs along a Roman road. Findings, with a 40 m and 20 degree matching rule: 5.0% of Great Britain's A-road length (2,346 of 46,684 km) follows a Roman line; England 6.5%, Wales 4.8%, Scotland 0.7%. Gloucestershire is the most Roman county (17.6%). The A5 has the most kilometres on a Roman line (135 km, Watling Street). Seen the other way round, 20% of the 11,578 km of Roman road in Itiner-e now lies under an A-road (28% of main routes). Sensitivity runs at 20, 80 and 150 m change the overall share (3.7% to 6.6%) but hardly the county ranking. Datum note: in Britain the Itiner-e lines sit about 100 m east of the modern roads known to follow them. Reading their coordinates as OSGB36 latitude and longitude (EPSG:4277) rather than WGS84 removes the offset (median gap on the A429 Fosse Way falls from 106 m to 8 m), and on Environment Agency lidar the corrected lines sit on surviving aggers. The analysis applies this correction; results_itinere_gb_corrected.geojson is the corrected file. Files: analysis.py (main analysis), counties.py (county boundaries), roman_cov.py (share of Roman road under A-roads), build.py and template.html (build the web page, index.html), data_itinere_gb.geojson (Itiner-e Britain subset, as published), data_osm_aroads.json.gz (OpenStreetMap A-roads, downloaded 26 October 2026 via the Overpass API), data_counties.geojson (ceremonial counties in England, preserved counties in Wales, council areas in Scotland, from ONS boundaries), results_*.json (results at 20, 40, 80 and 150 m), results_roman_coverage.json, results_itinere_gb_corrected.geojson, results_roman_aroads.geojson (A-road stretches on Roman lines), downham-lidar.jpg (lidar figure) and README.md. The interactive post is at https://tristan-hotham.github.io/how-roman-is-your-road/ and the code is on GitHub. Licences: code MIT; Itiner-e derived data CC BY 4.0 (de Soto et al. 2025); OpenStreetMap extract and the A-road results derived from it ODbL 1.0 (© OpenStreetMap contributors); boundaries and lidar figure Open Government Licence v3 (ONS, Environment Agency; contains OS data © Crown copyright and database right). AI use: I wrote the text, with drafting, data and coding help from Claude (Anthropic).