Image copyright Daniel Raven-Ellison Image caption Daniel Raven-Ellison measured his brain activity as he travelled

National Geographic explorer Daniel Raven-Ellison has just completed a 2.5 million step walk across Britain's cities and parks and electronically measured his changing mood with each step.

Wearing an EEG monitor strapped to his head he collected millions of snapshots of the activity in his brain as he crossed 69 cities over seven months in the UK from June last year.

The monitor measures the electrical activity of the brain from sensors located across key areas of the scalp.

Its software provided metrics on how stressed, relaxed, excited, focused, interested and engaged he was during his walks.

He says the monitor helped him become more aware of his response to his surroundings.

"You become more attuned to the things you find interesting, uninteresting, stressful, unstressful.

"If you scale that principle up that could be very powerful for the design of cities in the future."

Of course it is far from infallible and the readings can also be affected by many things beyond the environment.

Image copyright Daniel Raven-Ellison

Image copyright Daniel Raven-Ellison

A moment when his stress, excitement, focus and engagement levels peaked while walking across Cardiff was not down to its beauty but rather his need just at that moment to go to the toilet.

Climbing hills in the Lake District created stress, as did crossing busy dual carriageways, but the machine does not differentiate between experiences that are pleasurable and those that are not.

Although the monitor helped him become more aware of his surroundings, he said: "What's interesting is that for about half my walk across cities I'm not focused and I'm not actually in tune with my emotions."

However, the monitor did pick up on key times when his stress levels altered in line with his environment.

His trip across Cardiff started well, with low levels of stress as he began his walk in woodland, although he came across the more familiar sight of a pile of rubbish.

Indeed, fly-tipping was a recurring blight that seemed to prompt a rise in his stress levels.

Image copyright Daniel Raven-Ellison

Similarly each time he encountered a road, his stress and focus levels increased, whereas by contrast water had an immediate calming effect on him.

As he continued his walks, he often found himself alone although many cities could be crossed in around an hour or less.

In Aberdeen, its appeal was that much of his route followed an old railway line.

"It's full of interest and completely functional. Aberdeen as a walk just worked," he says.

Out of all the cities he visited, Swansea was one of his favourites to walk through as he described it as "surprisingly green with a ribbon of woodland".

Indeed, he was surprised by how green many cities are.

Image caption Swansea's green spaces were a surprise to Daniel

Image caption Sheffield was similarly mapped for its greenery

Elsewhere he found Newcastle to be the "best city for seeing children playing out in the wild" while in Wolverhampton he loved "Dudley with its hills and great views across the city".

If there was anything he could change immediately having travelled through so many cities on foot, he said: "I would speak to people about not putting dog poo in bags and adorning trees at head height for other people to pick up, it's all over the country and it's a shameful problem we need to deal with."

Most of his journeys began with either a rail or bus journey to the outskirts of a city.

Accommodation was often a tent or a B&B and given he is a vegan, he made more than a few visits to curry houses. To avoid blisters he put a plaster on the problem area before the walk.

For the most part the weather was good and perfect for his walks.

"I did have to protect my headset from the elements though, so always carried a sturdy umbrella with me," he said.

His walk, which began in June last year with a walk across St David's in Wales, ended in December in Birmingham.

Along with 69 cities, he also visited 15 national parks to compare urban and rural environments.

Having completed his trips, he said: "If lots of people were wearing these monitors it could inform how we build cities to make them less stressful and more interesting to walk."

Now he will upload the data to begin to build an "emotional" map of Britain and hopes others will follow.

"I'm going to be using the five million points of geolocated data to see how my emotions changed across different kinds of places.

"My plan is to release all of the data as open data, so that anyone can interpret it and present it in interesting ways."

The information is now going online.