STAC (SpatioTemporal Asset Catalog)

An open standard for describing geospatial data — where, when, and what, in a consistent JSON format any tool can read.

Why it matters

Before STAC, every data provider had its own metadata format. STAC lets one client (a browser, a script) search across NASA, ESA, Microsoft, commercial archives uniformly.

Where you’ll meet it

• NASA’s cloud archives expose STAC endpoints — LP DAAC publishes HLS and other land products through a STAC API you can query for items by area and date.
• Tools like pystac-client and the earthaccess library lean on STAC-style item/asset records to list the COG or NetCDF files that make up a scene.
• Each STAC “item” points at the actual assets (a HLS band as a COG, a thumbnail, metadata), so a notebook can pick exactly the file it needs without downloading the rest.
• It’s the connective tissue behind cross-provider mosaics — the same search shape works against NASA, Microsoft Planetary Computer, and ESA catalogs.

In plain terms

Like a library card catalog that every library in the world agreed to use — find a book the same way regardless of which library holds it.