How it works
A raster is a grid of pixels: an extent, a number of columns and rows, and a CRS that says
what the numbers mean. A file stores it in tiles (or strips, or chunks), so a reader can fetch
one piece without the rest, and in overviews, the same extent at half the resolution and half
again, so a reader zoomed out has fewer pixels to fetch.
Everything here comes from the header or the metadata: TIFF tags read with HTTP range
requests, Zarr's JSON, a WMTS capabilities document or an ArcGIS service's JSON. No pixel is
read. Unfold takes the grid from the globe to its own CRS, where it is a plain rectangle and
the coastline bends instead; stack the levels to see the pyramid.
Click the grid for the pixel and tile under the pointer at every level, with the tile's byte
range in a GeoTIFF, its chunk key in Zarr and its address in a tile service.