What best sums up London in 2017? The uncertainty created by Brexit? The cost of housing and its impact on a generation priced out of the property market? The invisible threat of poisonous NOx fumes? Or something more upbeat, such as the capital’s newly acquired status as a global food hotspot?

The answer, of course, is all of the above and more. London, teeming and diverse, is hard to sum up. But what if you had to? What if future generations were counting on you to encapsulate the essence of London today so they could understand and even experience it for themselves?

“In a global city of 8.8 million people, deciding what to preserve is challenging,” says Alex Werner, lead curator for the new Museum of London, which is scheduled to re-open in 2022 in Smithfield. “The museum has changed: today we try to capture the zeitgeist, how things feel at the moment, as opposed to simply collecting things that are gone or worn out.”

He outlines two approaches to contemporary collecting: “The first is more reflective. With the passage of time, 10 or 15 years, you look back and decide if you’ve missed something really important. The second involves taking a decision about something that’s happening now and going for it. An obvious example was the 2012 Olympics. This was a big, important moment for London, so we acquired in a number of areas.”

Many of the items that wind up in the Museum of London’s permanent collection are the result of specific projects. A recent exhibition on the Crossrail tunnel featured a small plaster statue of Saint Barbara that once stood on one of the tunnellers’ entrances; it has since found a home in one of the museum’s galleries. “Every tunneller would touch the saint as they went in for luck: she is the patron saint of tunnels,” says Werner, who likes the “ephemeral object [for its] interesting emotional power”.

Superstition, the plaster statue seems to suggest, survives even in 21st-century London. Saint Barbara makes a connection between today’s tunnellers and those who kept and honoured the religious icons of the past.

John Davis, Associate Professor of Modern History at Queen’s College, Oxford, believes archivists should be trying to capture Londoners’ lifestyles – what we eat, think, and buy – aspects of collecting that he feels were overlooked in the 1960s, his area of specialism. “I would like to see them capture the totality of London life rather than just institutional records,” he says, wondering who, for example, is keeping track of restaurant menus, or the website londonist.com.

Jason Webber, who is responsible for web archiving at the British Library, assures me that the whole londonist.com site is archived monthly, and the listings page daily, describing its features and guides to all aspects of life in London as a “superb resource”.  In addition, the British Library “sends out robots” once a year which attempt to download as many UK websites as they can identify. Anything with a .uk domain name and anything on a UK server is stored – up to two billion items every year, including many about London.

The idea is to replicate online what the British Library (one of six legal deposit libraries in the UK) does with offline materials, although Webber is aware that “we almost certainly miss quite a lot. We don’t even really know how much we don’t have.” The British Library has saved websites “on a small and selective basis” since 2004, but increased its digital activity in 2013, following legislation enabling it to archive and display in its reading rooms any material published online. “These websites are the letters, the journals, the newspapers, and the shop windows of our time.”

One glaring omission, however, is much of what is tweeted or written on Facebook, aside from a limited amount archived following permission from the person who wrote the posts, often a politician. “If you’re looking at 18th-century letters, you’re not going to get everything there, either,” Webber says. London frequently features in British Library special projects, such as the 7/7 bombings or the Olympics; the Library also archives “hyperlocal news sites” and Webber says anyone is welcome to nominate their own website to be saved for posterity.

Space is inevitably an issue when deciding what to keep. At the Geffrye Museum, which reflects the home life of the urban middle classes since the 1600s, Elyse Bell explains how curators cope with not being able to store any more items of furniture. “We have a testimony-based collection, which asks people for contextual information behind the piece they want to donate: its story, where they got it from, pictures of it being used. In the future, visitors won’t just stare at designer objects, they will have stories and memories about them.”

The museum collects photo­graphs, home movies, oral history interviews, questionnaires, diaries, floor plans, letters, and other documents, all of which it hopes will shed light on how Londoners lived in 2017. “Home is a concept that everyone can understand. We collect widely in terms of experiences, because we don’t know what people in the future will want to know about.”

Oral histories also feature widely at the London Metropolitan Archives (LMA), owned and managed by the City of London Corporation. The LMA collects personal stories to illustrate some of the different cultural and social groups living in London. “Our approach is two-pronged,” says the Head of Collections, Philippa Smith. “We make sure we have the official record of London today – we’re still collecting archives of important organisations, companies and official bodies based here – and we’re also making new connections with various communities and recording their stories.”

These include the archives for rukus!, a black LGBT arts organisation, which were acquired during a project, Speak Out, about the LGBTQ community. Smith says many groups come to the LMA with their own material, which tends to be “graphic, often photographs, or ephemeral: personal letters and diaries”.

How archives are preserved is as important as what gets preserved. “We keep them in a climate-controlled strong room, describing [the material] properly so people can find what’s there.” The shifting ways in which people are using archives is changing what the LMA does. “In academic research, there has been big growth in the digital humanities, using digital sources to write history. If we were cataloguing the records of a hospital, for example, we might now create a database with information that could be of use to a historian aiming to do more in-depth analysis of a kind that wouldn’t have been possible in the past.”

Purely electronic records have, however, yet to take off in a significant way. “We haven’t had any really big deposits that are solely electronic. We are still getting a lot of traditional archives.”

Vanessa Harding, Professor of London History at Birkbeck, warns that an excess of material poses its own problems. “When you are dealing with earlier history, the limited resources force you to be imaginative. With a wealth of sources, it can be more of a challenge to be properly critical and reflective of what it is you want to know, or how you choose your sources to tell the story you think is there. At the moment, if you said, ‘explain to me what London is like’, it would be hard to choose what to focus on.”

In a consumerist era, our throwaway objects no longer tell the sorts of stories they used to. “I’ve no idea how you would archive clothing and costume today: they’re so ephemeral,” Harding says. “Stats about how many items of clothing people own or how rapidly they change them may well be as important as what people were wearing. A Victorian dress would tell you something about its own life; now, an item of clothing might be worn only two or three times.”

The Museum of London’s Alex Werner notes that his colleagues are addressing this by collecting more than just the item in question. “The costume curator might collect an item and then commission a film about it, because the film will be as important as the object for interpretation in the future.”

Getting curators to think digitally is helping; this contrasts with the museum’s initial approach, which was to appoint someone to look after digital material. “In museums of the future you will see more film, more sound, and more recreated virtual worlds.”

For the 2012 Olympics collection, the Museum acquired some objects – a number of the costumes worn in the opening and closing ceremonies, for example – plus a series of tweets recording how people felt about the games. “We identified a series of people we called ‘Citizen Curators’.  Their day-by-day, hour-by-hour, minute-by-minute responses to the Olympics on Twitter have been added to the collection – all those emotional feelings on social media, for example about the venues being half-empty when we were trying to get tickets.” Two years later, the Citizen Curators project was displayed at The Photographers’ Gallery, where the tweets were linked to photographs. “We lent the tweets, like we lend objects to other museums.”

Brexit, in particular, is “haunting” the Museum of London, not least because of the prolonged uncertainty hanging over it. “We could collect some standard items, like protest banners,” Alex Werner says. “My niece attended that big BBC debate at Wembley, so we have her pass. But in 50 years’ time, when someone is doing a display about Brexit and what it meant, it could be that a film and oral history about how people felt would capture more than an object.”

Another challenging question is how to capture London as a sensory city. What does the capital sound and smell like? How does the Museum preserve a sense of the air quality or hidden pollution? The answer, Werner believes, could be “something like a map showing a day in the life of London on its main routes, with levels of pollutants rising in the rush hour. We could show how cars were killing our children.” He draws a parallel with objects that reveal how Londoners coped with smog in the 1950s, such as the flares people lit and held in front of buses to help their drivers to see.

Ultimately, curators and archivists have no choice but to accept their limitations in the face of mountains of material. In the same way that the LMA’s Philippa Smith is keen for people to bring their own material to be archived, and the British Library’s Jason Webber invites people to nominate their own websites for posterity, the Museum of London would like Londoners to suggest what they would like to see in a special collection for the new building.

This is nothing new, in fact: crowdsourcing has always been an aspect of its approach. When the Museum was established just over 100 years ago, letters in the Times appealed for items to be donated. “It’s part of our philosophy, that people should feel the collection belongs to Londoners,” says Werner.

Future generations are depending on the choices we all make.