Adds the official river dataset (国土数値情報 河川データセット, via the
Geoshape repository at 国立情報学研究所) as a second source alongside
OpenStreetMap, covering the 石狩川, 鵡川 and 沙流川 systems.
Main stems sit under their own 河川コード rather than the 「その他」 group,
so 夕張川, 鵡川, 穂別川, サヌシュッペ川 and both ウシャップ rivers had to be
fetched separately.
30 of 34 names appear in both sources; 29 of those agree on position to
within 110 m, which validates the projection method. Adds a source column
and notes the four that need care: 名称不明 and デチン沢川 (official only),
ホルカクルキ川 (no W05 counterpart at all), and サヌシュッペ川, which
parallels the road so the two datasets are tangent 5 km apart.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S6MpcBisZYhX45oDGRRJoz
Follows the pulse / pulse_dev split. 274.md keeps the frontmatter, the
intro and the lyrics workspace; everything below moves to 274-dev.md,
which will document how the PoI candidates were assembled and hold the
filtered charts.
Uses the new relative-Markdown-link convention rather than a siblings
macro, in both directions. Dev page carries publish: false to match
274.md while both are under wip/.
Contents moved verbatim; the dev page's own prose is still to be written.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S6MpcBisZYhX45oDGRRJoz
mikkeli