How much of a walking tour reaches the back row?

Pick a group size and see the group standing around its guide, drawn to scale. Tap any person to stand there. The photo on the right shrinks to the size a hand-held archive print looks from that spot.

People on the walk

The group at one stop, seen from above

Rings every 2 m from the guide. Dark dot: the guide with the photo. Yellow dot: you.

The archive photo from your spot

Dashed frame: front rowArchive photograph from about 1880 of the houses on Neuer Markt in front of St. Mary's Church in Berlin
Neuer Markt and St. Mary's Church around 1880, photographed by F. Albert Schwartz. Every house in it is gone.
People standing behind the second row

This is a model, not a measurement. It gives each person a standing space of 0.9 m by 0.9 m, which is a loose, comfortable group, and fans the rows out in front of the guide from 1.5 m. The photo is modelled as an A4 print, 30 cm wide; a bigger print scales every photo figure by the same factor. Sound from one speaker outdoors falls by about 6 decibels each time the distance doubles. A real pavement, a narrow bridge or a loud street makes a large group spread further than this.