mapterhorn-japan-bridge

An interim bridge that converts GSI's (国土地理院) 基盤地図情報 DEM data for Japan into a Mapterhorn-format terrain PMTiles archive (mapterhorn-japan-bridge.pmtiles), priority-merged from six GSI product types (1m, 5m×3, 10m×2) plus a global fallback — until upstream Mapterhorn's own Japan source (jpdem1a) catches up with the same GSI survey updates. Once it does, this whole effort is meant to be retirable.

Live preview: https://hfu.github.io/mapterhorn-japan-bridge/

What's in this repo

This repo is the documentation home and preview viewer only — no data-processing pipeline lives here. It holds:

• index.html / app.js / style.json — a MapLibre GL viewer for the current mapterhorn-japan-bridge.pmtiles build (3D terrain toggle included).
• CLAUDE.md — how the pipeline operates day to day.
• DECISIONS.md — architecture decision records (the why).
• HANDOVER.md — session-by-session narrative (the what happened).

A companion lineage archive, mapterhorn-japan-bridge-lineage.pmtiles, records — per pixel — which GSI source tier (1m/5m/10m/Copernicus fallback) won the priority merge, as a single-channel category layer served alongside the elevation data. A standalone globe-view showcase of it lives at hfu/japan-bridge-lineage (GitHub Pages).

The actual pipeline lives in a separate repo, hfu/mapterhorn — a fork of mapterhorn/mapterhorn, kept deliberately close to upstream. Source data comes from smartmaps/japan-geotiff-dem on Source Cooperative, itself produced by optgeo/japan-geotiff-dem.

Data

• Source: GSI (国土地理院) 基盤地図情報 DEM — 1m (DEM1A, airborne laser), 5m (DEM5A laser / DEM5B / DEM5C photogrammetry fallbacks), 10m (DEM10A / DEM10B), plus Copernicus GLO-30 as a universal fallback for areas GSI hasn't surveyed.
• Priority order: 1m > 5a > 5b > 5c > 10a > 10b > sea, merged at the pixel level (see DECISIONS.md D18/D20 for how and why).
• Format: PMTiles, Terrarium RGB elevation encoding.
• License / attribution: GSI data used under 測量法に基づく国土地理院長承認 (Approval for Reproduction pursuant to the Survey Act). See japan-geotiff-dem's own README for the current approval number and full attribution text — that repo is the canonical source for GSI-data licensing terms, not duplicated here.

License

Code and documentation in this repo (viewer, docs) are released under CC0 1.0 — public domain, no rights reserved. This does not apply to the GSI-derived elevation data itself, which carries its own Survey Act approval and attribution requirements (see above); CC0 here covers only what this specific repo contributes (the viewer code and documentation).