V215: where a photo was taken, in two columns a map can ask about.

phoenix_kit_files.latitude and longitude are the GPS position the photo's EXIF records, in decimal degrees (WGS 84: latitude -90..90, longitude -180..180), NULL for a file with none. They are columns, not part of the file's metadata, because a map asks "what is in this area?" and answers with an index.

The index is a GiST index on point(longitude, latitude), built into Postgres (no PostGIS, no extension to install, nothing to do with a named schema): a box on the map is one indexed lookup,

WHERE point(longitude, latitude) <@ box(point(west, south), point(east, north))

(PhoenixKit.Modules.Storage.Geo builds it, and splits a box that crosses the antimeridian in two). It is partial, over files that have a position, so a library of photos without GPS pays nothing for it.

The rest of the EXIF a photo carries (camera, lens, exposure, dates, altitude, speed, direction) is kept in metadata["exif"]; the position is both there and here, this being the copy that is indexed. No existing file is changed by this migration: the position of a photo already uploaded is read by Storage.read_exif/1.

Locks

ADD COLUMN of two nullable columns (no default, no rewrite) and a plain index build (the chain's convention, see V193), so writes to phoenix_kit_files wait while it builds; the index is partial, so it holds only the files with a position, and none yet. Re-runnable.