São Paulo is for sale. João Doria, mayor since 1 January, is planning to auction off South America's biggest city piece by piece: not only the racecourse, football stadium and carnival centre, but lighting, transport, health services and even the public funeral system. The glitzy promotional video is full of glass towers and night shots of glittering avenues; there’s no sign of the heaving lanes of traffic that blast and fume among concrete towers as far as the eye can see. There are few green or public spaces in São Paulo; the biggest, Ibirapuera Park, is now up for sale.

One way to keep track of the shifts in belief and allegiance as you walk through Beirut is by watching the walls. In the backstreets of Gemmayzeh and Ashrafieh in the east of the city, they are covered in stencil graffiti for the right-wing, Christian Lebanese Forces Party:

In his History of Contemporary Italy 1943-80, Paul Ginsborg quotes an American officer based in the peninsula after the war who found the skewed priorities of the natives rather disturbing: ‘The Italians can tell you the names of the ministers in the government but not the names of the favourite products of the celebrities of their country. In addition, the walls of the Italian cities are plastered more with political slogans than with commercial ones.’ In contemporary Bolivia the ratio of political slogans to commercial ones is at least ten to one, and that’s being generous to the ad hoardings.

Provenance and authenticity are always problems for art investors. How do you know it's the real thing? So much more of a problem when the work of art or otherwise is a stencil on a wall that appears overnight. Banksy has posed a difficulty to collectors – even if it's real, who owns that wall, and can I please take a chunk of it away? It has happened. These days you look for a Perspex covering to tell you if it's just some schmuck graffiti-ing the wall or a Banksy worth it's weight in gold bricks. Excitement followed by despair modulated by an upbeat local story then for North-West Londoners who found in Primrose Hill, Belsize Park and Kentish Town a series of grannies clasping kettles to their comfy bosoms next to the words: 'Make tea not war'. A most suitable image for the leafier parts of Camden.