# MarkableMap History: sources and processing

## Historical geometry and dates

- Dataset: Cliopatria, Seshat Global History Databank, pinned release **v0.2.0**.
- Authors/attribution: Ed Chalstrey, James Bennett, Erin Mutch and Cliopatria contributors.
- Repository: https://github.com/Seshat-Global-History-Databank/cliopatria/tree/v0.2.0
- Release archive: https://doi.org/10.5281/zenodo.20274630
- Paper: https://www.nature.com/articles/s41597-025-04516-9
- Download: https://raw.githubusercontent.com/Seshat-Global-History-Databank/cliopatria/v0.2.0/cliopatria.geojson.zip
- Licence: Creative Commons Attribution 4.0 International, https://creativecommons.org/licenses/by/4.0/ . See CLIOPATRIA-LICENSE.md.

The downloaded archive contains 13,765 records. This atlas includes its **13,380 POLITY records**, grouped into **1,550 distinct display names** after stripping surrounding parentheses. The 385 RELATION records are not displayed. This count differs from the source's general “over 1,600 entities” description because relationships are excluded and parenthesised composite names are normalised. Original record references, components, membership and inclusive date ranges remain available.

Years range from -3400 to 2024. Negative values mean BCE and positive values CE. Six source records end in year 0; this source value is retained in record descriptions. The interactive slider skips 0 because the historical BCE/CE convention has no year zero. A record ending in source year 0 is still shown for its applicable BCE years.

### Changes made by MarkableMap

`scripts/prepare-history.py` is the reproducible converter. Shapely simplifies each geometry with topology preservation at 0.035 degrees; coordinates are rounded to four decimal places. Polygon winding is normalised for D3. Identical source geometry is deduplicated within files. Files are grouped by century for world maps and by entity for empire timelines and fetched on demand. `index.json` contains the original archive's SHA-256, retained date and reference fields, and the entity catalogue.

Larger source records are drawn first, with smaller overlapping records on top. Composite empires and their member states can both be present. These colours are a display choice, not a legal judgement on sovereignty. Changes occur only at recorded dates; no interpolated boundaries are presented as fact.

Source geometry is not repaired by guessing historical territory. Coverage is uneven and can contain omissions and inconsistencies. **The British Empire series is 1706–1999**, not a complete reconstruction of all British possessions from their beginnings. For example, the source represents Commonwealth of Australia separately after 1901, and Australia is absent from the British Empire composite in 1920. Dominion, protectorate and dependency definitions change over time. **Roman Empire is 31 BCE–394 CE**; successors are separate entries. Empty years remain empty.

## Coastline context

Natural Earth 1:110m land, pinned v5.1.2:
https://raw.githubusercontent.com/nvkelso/natural-earth-vector/v5.1.2/geojson/ne_110m_land.geojson

Public domain: https://www.naturalearthdata.com/about/terms-of-use/

Modern coastline is context only. It is not a historical shoreline reconstruction.

## Software

D3 v7.9.0: https://github.com/d3/d3/tree/v7.9.0 — ISC licence in `../vendor/d3-LICENSE`.

SVG is the shared source for the live map, image exports, printing and canvas video frames. The browser's MediaRecorder encodes MP4 when supported, otherwise WebM. No paid APIs, geographic lookup service or remote video rendering are used.