If you live in Southwark or Tower Hamlets (Canary Wharf) you can probably guess at the tallest structure in your borough. But what of the others?
The answers are often surprising. Not every borough is dominated by high-rise glass and steel apartment blocks or commercial towers. In some regions, chimneys or communication masts win the crown. There's also a stadium and a power station in the mix. Some boroughs are so low-rise that churches still dominate the skyline.
Barking and Dagenham
The Lemonade Building: This memorably named tower is the pinnacle of a modern housing development in central Barking. At just 58 metres, it's one of the smaller 'tallest' in our list.
Hendon Waterside: The Vista is the tallest block in this 2016-completed residential development, overlooking the Welsh Harp reservoir. At 85 metres, the tower supplants the 54 metre St Jude-on-the-Hill as the borough's tallest.
Marlowe House: This 56 metre tower block near Sidcup station dates from 1966.
Wembley Stadium: The famous arch dominates the skyline of north-west London, and it's no surprise to find it's the tallest structure in Brent at 133 metres. You could stack three Emirates Stadiums in the same height.
Crystal Palace Transmitter: Who'd have guessed that the Borough of Bromley plays host to London's fifth tallest structure? The 1950's telecommunications mast stands 222 metres tall.
BT Tower: Formerly the Post Office Tower, this iconic peak of Fitzrovia reaches 177 metres or 190 metres if you include the antennae — much taller than anything nearby.
City of London
The Heron Tower: At 230 metres, the Heron Tower narrowly beats the Cheesegrater (225 metres) to the title of the City's tallest. It will be surpassed by upcoming developments such as 22 Bishopsgate.
Croydon Transmitter: You probably know it as 'the other big mast thing at Crystal Palace' but this telecommunication tower actually stands on Beulah Hill in the Borough of Croydon. At 152 metres, it's a fair bit smaller than its more famous sibling (219 m).
Apex Tower: This newbuild residential block overlooking Ealing Green stands 76 metres tall, finally beating longtime record holders the Rufford Tower and Moreton Tower in Acton (shown above), each of 61 metres. (Thanks to James P for this update.)
Edmonton Refuse Incinerator: Enfield's peak is an industrial building, completed in 1971. The chimney stretches 100 metres into the sky.
The Waterman: At 99 metres, this recently completed residential building is a shade taller than the masts of the O2. Other new developments on the peninsula may overtake it soon. (Thanks to Woolwich Art & History for this correction.)
Skyline: This residential tower at Woodberry Down rises some 101 metres, making it the tallest in Hackney. But not for long. As the towers of the Square Mile spill over the border into Shoreditch, other peaks will soon overtake it.
Hammersmith and Fulham
Empress State Building: At 117 metres tall, this Earl's Court landmark is a mere quarter the height of its New York namesake. Still, it's enough to make it the tallest building in this borough.
Alexandra Palace Transmitter: The familiar mast of Ally Pally looks all the taller for standing on a great big hill. It's 67 metres tall.
Kodak Chimney: The old Kodak factory near Harrow & Wealdstone station may have closed down, but its landmark chimney remains, towering 57 metres. The rest of the Kodak complex is to be redeveloped into housing, but the chimney will remain as a reminder of the area's 125-year links with the camera firm. The chimney is likely to lose its status as the borough's tallest structure soon, with plans for a 134 residential tower as part of the Harrow Square development. (Thanks to Martin Frewer for the information.)
Mercury House: This rather squat looking commercial office building in Romford stands 57 metres tall.
Heathrow Control Tower: Completed in 2005, this distinctive control tower dominates the skyline of the otherwise flat borough at 87 metres tall. A much smaller version can be found in the Wetherspoon's in Terminal 2.
The Tower at GWQ: Hounslow's tallest is the 75 metre residential tower on the northern edge of Brentford — an area recently dubbed the Great West Quarter (hence the name).
The Lexicon: The loftiest of a new parade of skyscrapers along City Road. The Lexicon was completed in early 2017 and stands 117 metres.
Kensington and Chelsea
Trellick Tower: The brutalist icon was completed in 1972 and remains the tallest building in the borough at 98 metres.
Kingston upon Thames
Tolworth Tower: This much maligned 1964 commercial building totally dominates the skyline in these parts — there's nothing nearly as big as this 81 metre beast for miles.
St George Wharf Tower: Many towers are springing up in Nine Elms. This tubular skyscraper was the first and biggest of this new wave. It rises 181 metres, making it (for now) the tallest residential building in London.
SELCHP: That's South East London Combined Heat and Power Plant when spelled out in full. You've probably noticed the 100 metre chimney near Millwall's ground in south-east London. It's a massive waste incinerator, built in the mid-90s.
The Tower: The borough of Merton doesn't contain many high buildings. It's tallest at 54 metres, next to Colliers Wood tube station, is somewhat notorious though, thanks to its bleak concrete facade. The despised building recently underwent a makeover (above) and is now mostly harmless.
150 High Street: Stratford's skyline is changing rapidly. This curvy skyscraper, also known as the Halo, is currently the tallest at 133 metres. It will soon be surpassed by the Manhattan Loft Gardens.
Pioneer Point: This 105 metre residential skyscraper dominates the skies of North Ilford and is visible for miles around. It is unusually tall for a building in outer London and stands beside another residential tower that, at 82 metres, would tip the scales in many other boroughs.
Richmond upon Thames
St Matthias' Church: One of two boroughs whose tallest buildings are churches. St Matthias can be found in central Richmond with a spire that climbs 61 metres. Incidentally, the Pagoda in Kew Gardens is the borough's second tallest building, which shows what a low-rise part of town Richmond is.
The Shard: At almost 310 metres, the Shard is not only the tallest building in Southwark, but also the loftiest in the whole of western Europe. Surprisingly, though, there are taller structures elsewhere in the UK.
Quadrant House: The otherwise unremarkable office block beside Sutton station was completed in 1980, as you might guess from the turd brown colour.
One Canada Square: The pyramid-topped skyscraper at Canary Wharf was the tallest in London from 1991 until 2012, when it was overtaken by the Shard. It stands 235 metres, but two slightly taller towers are now under construction.
Northwood Tower: Waltham Forest's skyline was once much beefier. In recent years, some two dozen tower blocks over 50 metres have been demolished. Where it was once the 15th tallest block in the borough, Northwood near Wood Street station is now the loftiest at 57 metres.
Battersea Power Station: Reaching 113 metres, the famous power station was the first London structure to surpass St Paul's in height (though the latter appears taller thanks to its position on Ludgate Hill). 80 years on, it barely makes it into the top 50 tallest structures in London, but it is the highest in Wandsworth. For now.
Millbank Tower: This 1960s behemoth dominates the skyline between Tate Britain and the Houses of Parliament. In its time, this was one of the tallest structures in London. Nowadays, it doesn't even make the top 40. It stands 119 metres.
Sources: Most of the information comes from the Emporis website, which handily lists the tallest structures in most of the boroughs. A list of tall buildings on Wikipedia was also useful for ranking heights across boroughs. Our list incorporates both buildings and more general structures like communication masts.