photographs

Flickr only 20,274 + Commons, iNaturalist 42,394 Mapillary street-level 350,015
a separate layer, not part of the map above: 87% of it is five organisational camera fleets, so it draws the road network rather than where people photograph

who

local
photographed in Hanoi over a span of a month or more tourist
a local of some other city, in Hanoi under a month unknown
photographed nowhere over a span of a month

marks

popularity squares
one per 63 m cell, side set by how many different photographers of that colour shot there, nothing for a lone one connecting lines
one photographer's consecutive photos, within 10 min and 15,000 ft

The method and the look are Erica Fischer's Locals and Tourists, 2010. Fischer computed a Hanoi box and never published its map. This is a reimplementation: source and method.
Basemap © OpenStreetMap contributors (ODbL). Photo metadata from YFCC100M, Wikimedia Commons and iNaturalist; photographs are © their photographers.