The map is based on the large scale Ordnance Survey maps of the city of London published starting in 1871. It has been edited and colorized, and the text "Music Hall" added, and the building marked in red. The original map shows boundaries clearly but the buildings are unnumbered. 
The location of the hall is shown in Baedecker's London and its Environs which shows it set in from the street, at the end of the passage (Karl Baedeker, London and its Environs, Handbook for Travelers, multiple editions, 1877-), and agrees with the 1882 Post Office London Directory, which lists public houses at number 1 and number 18, corresponding to  the buildings on the north side of Store street marked "P. H." on the map, and a Postal Telegraph office at the corner with Alfred Place. The directory also lists piano manufacturers Schucht &amp; Schoenewald at number 14, and Charles Jackson &amp; Co at number 13.

This corresponds to the position marked in less detailed maps such as  Philip's new plan of London  (George Philip &amp; Son, London &amp; Liverpool, 1873). It also matches the given location of "Music Hall", Store Street on the Map of London, 1868 by Edward Weller F.R.G.S. This mapping evidence goes contrary to the account on the owner, piano manufacturer Robert Wornum, by piano historian C. F. Colt  (C. F. Colt. The Early Piano Stainer &amp; Bell, London. 1981) where he stated that the site is occupied by the Building Centre, which moved to number 26, on the south side of Store street from 9 Conduit street in 1952.
City of London, 1:2,500 scale, sheet 34  Ordnance Survey, 1875
Ordnance Survey; traced, edited and colorized by User:Mireut