Terrain Tiles — locally rendered relief for Cha.fyi

Terrain: Mapzen / Tilezen · USGS · NOAA
https://registry.opendata.aws/terrain-tiles/
https://github.com/tilezen/joerd/blob/master/docs/attribution.md

Actual underlying source families identified in the downloaded tile HTTP metadata:

SRTM and GMTED2010 terrain data courtesy of the U.S. Geological Survey.

ETOPO1: DOC/NOAA/NESDIS/NCEI — National Centers for Environmental
Information, NESDIS, NOAA, U.S. Department of Commerce.

Mapzen Terrain Tiles distributed through the AWS Open Data program;
Tilezen/joerd terrain processing. Accessed 20 October 2026.

U.S. Government source material is not subject to copyright protection in the
United States. Source-specific terms, including the SRTM international notice,
are documented in the attribution reference linked above. This file does not
replace those terms or imply USGS/NOAA endorsement.

Modifications: elevation values decoded from Terrarium RGB into metres;
tiles mosaicked, bilinearly resampled, lightly smoothed, and rendered as
multi-direction grayscale hillshade with a subtle elevation wash. Slopes use
1.2–2.0× vertical exaggeration according to view scale for legibility; this does
not add geographic features or increase source resolution. Negative bathymetry
is flattened for the land-relief display. WebP is a compressed display image,
not an analytical DEM.

Sampling, not promised accuracy: source tile spacing varies by zoom and latitude.
SRTM is approximately 30 m sampled (Tilezen notes 90 m nominal quality); GMTED2010
and ETOPO1 are coarser. No artificial terrain or finer-detail enhancement is used.
These small context illustrations are not navigation maps.

Full viewport bounds, source zoom, imagery-source names, rendering settings and
asset hashes are recorded in manifest.json. Raw elevation tiles are cached
privately in research/terrain-cache and are not needed by website visitors.

Coastline: Natural Earth, 1:10m physical land data (public domain).
https://www.naturalearthdata.com/about/terms-of-use/
Reprojected into normalized Web Mercator for the SVG coastline overlay.

Supplemental mountain labels: documented representative locations, not range boundaries.
Names and coordinates checked against the following geographic and scientific sources:

Alishan Range
https://eng.taiwan.net.tw/m1.aspx?id=247&sno=0000208
https://www.ali-nsa.net/mountain/zh-tw/about

Xueshan Range
https://landscape.forest.gov.tw/Front/land_search/Landscape.aspx?Sn=214&id=kVsq7hIIvoI%3D

Yushan Range
https://landscape.forest.gov.tw/Front/land_search/Landscape.aspx?Sn=170&id=kVsq7hIIvoI%3D
https://www.ysnp.gov.tw/StaticPage/Terrain

Ailao Mountains
https://www.chinaflux.org/gczd/index.aspx?nodeid=155

Wuliang Mountains
https://alf.cern.ac.cn/content?id=47903
https://lcj.yn.gov.cn/special/2025/0313/6406.html