Location map archive for the Apple logic board 820-01598, following Apple's 820-xxxxx board numbering printed on the PCB. A location map shows where components sit on the board, helping to find capacitors, resistors, ICs and test points referenced in a schematic when diagnosing shorts or missing power rails. The contents are packed in RAR form, so the exact viewer depends on the files inside, commonly images or PDFs. Confirm the 820 number on your board matches before relying on part positions.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @fixtronix. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.