Mayors love buildings. They love the opportunities to pose in hard hats, to make their mark on their cities, to leave permanent monuments of their reigns and to demonstrate in the most tangible possible way that Something Is Being Done. Mayors have also been known to use large contracts and profitable planning consents to return favours to their supporters in construction and development and, in some disreputable cases, to take kickbacks themselves.

London mayors have more reasons than most to like planning, architecture and design, as these are areas within their relatively limited range of powers where they have some influence. They oversee the London plan, which guides the future development of the city, and have the power to approve or refuse significant planning applications. They have budgets that can be spent on the city's public spaces.

Ken Livingstone, in his last incarnation as London mayor, pursued a policy of unstoppable growth, based on his belief, since discarded, in the permanent revolution of financial services. Nothing should stand in the way of developers erecting buildings that would serve the banks that would make the money, a portion of which could then be extracted to pay for the affordable housing that was made more necessary by the high property prices caused by the boom in financial services.

He adopted Richard Rogers's idea of the "compact city", that it was good to densify and intensify the centre of London, rather than let it sprawl horizontally into the green belt. The results of his dash for growth, combined with the compact city, were a series of towers pushed through the planning system with Livingstone's support: some, such as the Shard, are now being completed; some are poking their concrete lift cores into the air; some remain computer-generated images awaiting the funds to be turned into reality. Livingstone also pursued, with partial success, a policy of creating "100 public spaces", based on Barcelona's renewal of its streets and squares.

Then came Boris Johnson, who has shown himself as much in love with grand gestures as anyone, although with limited funds to achieve them. He has therefore thrown himself behind the London River Park, a privately financed plan for a series of pontoons floating in the Thames that, while they will have some benches and green stuff here and there, will also have extensive corporate hospitality areas to pay for the project. He backed the Emirates Air Line, a cable car that may or may not be functioning in time for the Olympics, in return for sponsorship which means that the airline will get its name on the tube map. He has slathered the streets with blue cycle lanes, a colour by happy coincidence close to the branding of the sponsor of Boris bikes, Barclays Bank.

He has promoted the Orbit, the 115m-high sculpture by Anish Kapoor next to the Olympic stadium, which reportedly arose from a chat between Boris and its sponsor, Lakshmi Mittal, in the gents' at the World Economic Forum in Davos. And, indeed, unless there is some so far hidden genius to this structure, which will reveal itself once the public is allowed to explore it, it currently looks to me very much like a lot of steel and money pissed into the sky, to no great purpose except the vanity of those involved. Johnson has presented images of the Eiffel Tower visible above Parisian apartment blocks and sincerely seems to believe that the Orbit will be no less impressive seen from the future residential developments on the Olympic site. I doubt it.

He has also backed the revival of the Routemaster bus, with the admirable intention of bringing back a bit of dignity and civility to public transport. These handsome if over-styled objects certainly lift the spirits in rare sightings along the 38 route – there are eight currently in operation – but until they become the standard rather than the exception they will remain in the category of rhetorical flourish.

But if Johnson's monuments suffer from the columnist's love of making a splash, his mayoralty has been more impressive when it comes to things that are barely visible, or about taking stuff away rather than adding it. Recently, without much discussion or brouhaha, railings and barriers disappeared from London's major roads, as part of a programme of "decluttering". The theory is that if pedestrians and cars are less nannied by safety features, they will take greater responsibility for their own actions and behave more safely, with the added benefit that the streets look much better.

The experience of High Street Kensington, which was decluttered some years ago, suggests that it works. No one yet knows for sure if the changes to London's other roads will save lives or cause carnage of Charge of the Light Brigade proportions, and if it's the latter it will come to seem like a very bad idea. Assuming it does not, decluttering represents a significant change in attitude to city streets – they are seen more as places to inhabit than as machines for channelling the movement of people and cars.

Slightly more visible are the removal of the gyratory systems at Piccadilly Circus and elsewhere, and the X-shaped pedestrian crossing at Oxford Circus, devices that rebalance the relationship of pedestrians to vehicles in favour of the former. There is also the remaking of Exhibition Road, an impressive if partly compromised attempt to realise the concept of a "shared surface", where people coexist with cars, on a large scale.

Johnson's officers have been trying to direct limited funds towards reviving London's more obscure zones. There are officially 600 high streets in the capital, and Johnson has available £250m or so to spend on improving them, which works out at less than half a million per high street, which isn't very much. The idea, therefore, is to do a lot with a little, to connect better the suburb of Rainham, for example, with its beautiful marshes; to put up a new sign on the library on Ponders End; to make a street market work better; to spruce up the lesser-known parks. It is arguably the closest any Tory politician has come to realising the fast fading idea of the Big Society.

It's not all that much, but it is in principle an intelligent use of scarce resources and is more effective than a grand plan of Livingstone's for an area called Barking Riverside. This would have used up more than twice the budget at Johnson's disposal for the whole of London on the infrastructure necessary to make it work. Meanwhile Johnson has also introduced minimum standards of space for new homes, including such things as balconies that are large enough to have some use. Developers predicted that this interference with their right to design very mean homes would make house building altogether impossible, but it has not turned out to be the case. Whatever the problems currently afflicting the construction industry, this has turned out to be the least of them.

As for skyscrapers, the recession has reduced the number of controversial proposals landing on Johnson's desk, although he did turn down a ridiculous plan for a huge glass funnel next to Battersea Power Station. On this occasion he resisted the temptation to identify himself with a pointless spike.

This, then, is Borisopolis: a combination of show-off whatsits and fairly sensible stuff. When it comes to public space there is not a fundamental difference between Labour and Tory, Livingstone and Johnson. Both think it's a Good Thing and both have an idea of a city that favours pedestrians and cyclists more than it did before. Johnson and his administration do however deserve credit for getting some things done that make London, in a modest way, a better place to live.