General election 2017: The maps that reveal where this election could be won - BBC News
What exactly can we tell about where the party leaders have been out to win votes?
Tim Farron, leader of the Liberal Democrats, campaigning in Kingston and Surbiton

The 2015 election result was a bit of a surprise. Pollsters got it wrong - and so did the media. Had we paid closer attention to where the Conservative Party was choosing to campaign, we might have spotted a gap between polling forecasts and Tory ambitions. We might have noticed David Cameron was fighting in the sort of seats that implied he thought a victory was coming.

This time, we hope to avoid that sort of mistake by paying closer attention to the campaigns. Here is Conservative leader Theresa May's journey since the prime minister called the snap general election on 18 April. As of Monday, she had taken trips all over the country, the purpose of which is to get her face on local TV and in local newspapers.

NOTE: The maps for Theresa May, Jeremy Corbyn, Nicola Sturgeon and Tim Farron have been updated to include visits made up to 7 June, the final day of election campaigning. You can read further analysis on those visits here. We are waiting on more information surrounding Paul Nuttall's campaign.

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Labour leader Jeremy Corbyn, too, has been all over Great Britain. The two leaders have covered a lot of ground - but not quite the same sorts of places.

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To help you understand this pattern, below is a chart explaining the significance of where these two have been.

Theresa May has so far been visiting seats with a considerable Labour majority but where UKIP also did well in the 2015 elections

See how Mrs May is visiting seats which have some very big Labour majorities - look at Leeds East. But she is targeting Labour seats with big UKIP voter populations, where hoovering up the UKIP vote can do much of the work of taking the seat off Labour. In Dudley North, UKIP votes would be enough to take the seat on their own.

See also how Mrs May is largely not visiting the same sorts of places as Mr Corbyn. She is fighting in places which imply she wants a three-digit majority. The Labour Party either regards the "front line" as being nowhere near so gloomy for them or they are choosing not to deploy Mr Corbyn into their front line. If Labour were winning in Harlow, where Mr Corbyn went to campaign, it would probably be winning a majority.

What, then of the other leaders? Liberal Democrat leader Tim Farron has been clocking up the miles.

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The Lib Dems' strong pro-EU stance now distinguishes them from other UK-wide parties. So far, Mr Farron has only been to one seat that, according to academic estimates, voted Leave in the EU referendum - the Lib Dem-held Carshalton & Wallington. And 14 of the 20 places he's visited had Remain votes in excess of 60%.

The map shows he's hoping to take seats from both Labour and the SNP. The really big questions about the Lib Dems' future, however, are in their fight with the Tories.

Both Theresa May and Tim Farron have visited the marginal seat of Lewes in the early stage of this election campaign

In the Tory-Labour battleground, Mrs May and Mr Corbyn seemed to be fighting different elections. In the Tory-Lib Dem fight, both parties seem to think the election is going to be largely about Lib Dems taking seats back from the Tories. Both went to marginal Lewes, for example.

Mr Farron has paid a visit to Oxford West & Abingdon, for example, and Mrs May has been to shore up support in St Austell & Newquay. Both are current Tory seats taken from the Lib Dems.

But the Lib Dems' meagre resources will be spread thin at this election. It is not a by-election. The Tories are also polling well - and just look at the three seats above the dotted line. Those three seats - Norfolk North, Carshalton & Wallington and Southport - could all be taken by the Tories if they can win over UKIP voters. And the Tories have already started advertising in the Southport local press.

This video can not be played To play this video you need to enable JavaScript in your browser. Newsnight Policy Editor Chris Cook talks through the Conservative and Labour battleground chart in more detail

The Scottish National Party has started its roadshow, too. The party won so many seats in 2015, there is no choice but for them to run a defensive election. We cannot see where leader Nicola Sturgeon is worried about quite yet. Let's come back to them.

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UKIP, meanwhile, has had a slow start. We will have to wait a bit more before we can say much more.

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The thing that jumps out at the moment is the scale of the Tories' ambitions against Labour. There are important questions about how campaigning works and how parties get their messages out, to which we will return during the campaign - along with updates to these maps and graphs.

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Maps display winning parties from 2015 general election or most recent by-election. Estimated figures for the 2016 EU referendum are from Dr Chris Hanretty's academic study that remapped results from the EU referendum from local authority level to parliamentary constituency level. Leader visits displayed on the maps are accurate up to Monday 8 May, and include only visits related to the 2017 general election campaign. Maps built with Carto.