England’s modern system of elected mayors was first introduced by the Blair government. London was first out of the trap, electing Ken Livingstone – at that point an independent who didn’t keep banging on about Hitler – in 2000.

But other places soon followed. At first they were most relatively small places – a couple of mid-sized cities like Middlesbrough and Stoke; some smaller towns; some boroughs that make up parts of other cities (Hackney, North Tyneside). The bigger cities appeared later: Leicester in 2011; Bristol and Liverpool the following year.

Matthew Smith, formerly of the think tank Policy exchange, has turned all this into a graphic you can use to track which cities have mayors, and who they voted for in each year since 2016. You can play with it below.

Two trends jump out at you. One is that mayors are a lot more likely to be independents (grey, on the graphic) than most elected politicians in Britain. Partly this is probably the nature of the role.

But it may reflect something else, too. In more recent years – as the recent elections in London and Bristol highlight – the Labour party has come to dominate the mayoralties. That’s probably because Labour has increasingly become the party of urban Britain – but when it was in national government, people were less inclined to vote for it in local elections. Since the residents of, say, Middlesbrough were never likely to vote Tory, though, they seem to have opted for an independent instead.

The other trend is that some cities, er, changed their mind. Stoke’s mayoralty was abolished in 2010. Hartlepool’s mayor Stuart Drummond had proved surprisingly successful (he served three terms), despite having originally been elected in the guise of a football mascot, H’Angus the Monkey, in 2002 – but this didn’t stop the town abolishing the post altogether in 2014.

More to the point, perhaps, the vast, vast majority of English towns, cities and boroughs never bothered creating them in the first place. I think that’s what one might call a “mixed picture”.

At present, there are, by my count, 17 elected mayoralties in England. But that number will increase substantially – how substantially we don’t yet know – when the new metro mayors are created in May next year. This graphic is about to get a lot more crowded.

Here it is. Have a play.