HK ChronoMap 維城時空 — Historical GeoTIFF Explorer & PWA

Reclamation Detector 填海探測 22.2842°N, 114.1551°E

1889 Original Shoreline (Land)

District No. 5 Choong Wan — Historic street grid between Queen's Rd & Praya Central.

HK80 Grid: 834020 E, 816190 N

How to Automate 300 MB GeoTIFFs with GitHub Actions + Cloudflare R2

Zero manual uploads • Bypasses GitHub's 100 MB file limit • Instant mobile PWA tile streaming

Direct Answer: Do NOT manually upload 300 MB .tif files to GitHub!

1. Why raw TIFs fail on web/GitHub: GitHub rejects files over 100 MB (your City_of_Victoria_HongKong1889.tif is 298 MB), and iOS/Android browsers cannot render a 15,280×6,699 uncompressed TIFF without crashing memory.
2. Two Smart Solutions: • Option A (Zero Storage / Instant): In your progress.txt, notice that Data.gov.hk lists 14 "CSDI Portal API Available" links alongside the 11 GeoTIFFs! Those CSDI APIs already serve pre-sliced XYZ/WMTS map tiles over HTTPS for free.
• Option B (Full Custom Control + Offline PWA Packs via GitHub Actions + Cloudflare R2): Let a GitHub Actions runner automatically download the .zip files from Data.gov.hk, unzip them on GitHub's 14 GB temp SSD, run gdalwarp to reproject from HK1980 Grid (EPSG:2326) to Web Mercator (EPSG:3857), slice them into tiny 25 KB WebP tiles (or a single `.pmtiles` archive), and push them straight to Cloudflare R2 (10 GB free, $0 bandwidth fees)!

STEP 1 • DATA.GOV.HK

Fetch 37 MB .zip

GitHub Action runs curl -L using the Data.gov.hk resource IDs from your progress.txt & unzips the 298 MB GeoTIFF in temp storage.

STEP 2 • GDAL REPROJECT

EPSG:2326 → 3857

gdalwarp converts Hong Kong 1980 Grid coordinates into standard GPS Web Mercator & makes black collars transparent.

STEP 3 • WEBP PYRAMID

298 MB → 25 KB Tiles

gdal2tiles.py --webp slices the giant image into zoom levels 12–20 so phones only download the 6 tiles on screen (~150 KB).

STEP 4 • CLOUDFLARE R2

Global Edge + PWA

Tiles upload to Cloudflare R2 via AWS S3 CLI, while your HTML/JS app deploys to Cloudflare Pages with Service Worker offline caching.

Offline Hiking & Heritage Tile Packs (PWA)

Pre-cache compressed WebP tiles into iOS/Android IndexedDB

Instead of forcing users to download a 298 MB raw GeoTIFF, slicing into WebP tiles shrinks each historical map pack by 97% so hikers in Tai O, Sha Tin, or Lei Yue Mun can use GPS offline with zero cell signal:

iOS Safari & Android Chrome: Tap Share → Add to Home Screen CacheStorage Ready

Pro-Tip: The 14 CSDI Portal APIs in your progress.txt

Stream pre-tiled historical maps directly from Hong Kong CSDI Government servers

In your progress.txt, items 12–25 are marked "(CSDI Portal) API Available". The Hong Kong Lands Department & CSDI Portal actually host OGC WMTS / XYZ map tile endpoints for every single one of these historical maps!

That means you can combine Cloudflare R2 (for custom ultra-high-zoom WebP overlays & offline packs) with CSDI's live API endpoints as a zero-cost fallback.

https://api.csdi.gov.hk/apim/dataquery/api/?id=landsd_rcd_1638867975043_84863&layer=hm_1889&style=default&tilematrixset=EPSG%3A3857&Service=WMTS&Request=GetTile&Version=1.0.0&Format=image%2Fpng&TileMatrix={z}&TileCol={x}&TileRow={y}

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