Outside it's 30 degrees, there are banana plantations as far as the eye can see, cut only by single track roads rising up into the distance. In the front seat of our oven-baked mini bus an American man attempts to use his iPhone to snap a photo of a road sign while balancing a laptop precariously on his knee with his free hand.

One of his astute cartographer's eyes peers at the speed sign he's photographing while the other focuses on some complicated looking mapping software on the computer screen.

With the part of his brain not currently occupied by circus trickery, he's explaining to seven tech writers what all this multi tasking is for. This, we are told, is how TomTom's sat nav maps are made.

For a lot us in the van, what's happening is a revelation. Although none of us are saying it out loud, we're all asking ourselves why there isn't a machine that takes care of all of this?

It seems wildly unmanageable to have real people whizzing around the planet, making real edits to maps on a global scale. But that is, in part, what happens every day. It's the unseen work of a vast network of TomTom field agents that means we can all sucker a little box to our car windscreens and get from A to B with the minimum of fuss.

The road our American friend and TomTom field-mapping specialist Tom is tweaking today, is on the Caribbean island of Martinique. We're here to see the mapping process in action at the launch of TomTom's Map Paradise campaign.

Martinique offers a unique insight because it's virtually unmapped on TomTom's system. It's a chance to see first hand how the multi-layered information like speed limits, one-way streets and points of interest are compiled, often litterally from the ground up and end up our devices.

So where do we start? Just as they would have done with the UK, TomTom source orginal from governments, combine those with ordinance survey and existing aerial maps to create a very basic geometric footprint.

This forms the foundation and for Martinique, it becomes instantly clear that these base maps are badly lacking in detail. Road names are missing, speed limits are scant and even some roundabouts are unmarked.

In most cases where there's such patchy information, TomTom would dispatch a special mobile mapping van - think Google's cars. These come loaded with the latest mapping tech including a Ladbybug 360 camera, 3D gyropscope, differential GPS, a laptop and a - unsurprisingly, a TomTom sat nav.
 
In addition to capturing detail with 360 photography, the sat nav itself acts as a GPS 'probe', creating a trace that's viewable on special software. Essentially a line of the real journey overlaid on the original map, this trace helps highlight the corrrect co-ordinates of the road and lets experts see in seconds that the road positioning on the base map are out. It also helps spot where new roads may have been built.
 
Each TomTom sat nav or Personal Navigation Device (PND) works in a similar way. They come loaded with the option to share data anonymously and if you're one of the 90 per cent of TomTom owners who agreed to transmit your journeys, then everytime you fire up your sat nav, you're acting as your very own 'probe'.

When you link your TomTom to your PC to update the maps, your GPS information is sent back to TomTom. Or if you own one of the newer wireless models then this happens in realtime over the air.

All this trace information from the probes and the camera footage fired back from these vans is sent to India where up to 900 people interpret and quality check the updates.

This constant stream of camera footage and probe data from mapping vans, owners sat navs and field agents is all vital in helping TomTom identify where road systems are changing. This in turn helps target where to send the vans next based on higher levels of changing information that means an area might need a significant update.

Sadly today we're not in one of those hi-tech vehicles. Instead we're sampling the more hands-on work that TomTom's network of field agents do on a daily basis.

We're armed with a laptop, sat nav and a special iPhone app that enables us to snap road signs, points of interest and road changes and submit them to TomTom's mammoth database on the move.

The laptop is also pre-loaded with the same Cartopia mapping software that allows us to view probe data and suggest adjustments to TomTom's base maps while we're still in the field.
 
We're also shown how anyone can submit a suggested change using the TomTom's Map Share function. This piece of funcationality turns everyone into a potential field agent. This community reporting adds another 250,000 updates to their database every month and is another key part of keeping the maps detail up-to-date and of a higher value.

TomTom also has access to huge amounts of anonymous mobile data - the kind the CIA might use to triangluate your position if you were Will Smith in Enemy of the State. This information details where there are high densities of mobile signals, how fast they're moving and in which direction.

It's the same data that powers HD traffic and while it's not as accurate as a GPS probe, particularly in cities where traffic moves at the same speed as a pedestrian with a phone, but it still gives huge insight into traffic speeds and motorist's behaviour that helps shape the maps.

While the enormous amount of mobile and sat nav data helps build out the bigger picture, field agent reports are key to the finer detail. The level of information you need to gather is truly mind boggling and it's amazing to watch someone like Tom at work.

Over a single stretch of road he shows us how to use the sat nav to add changes and snaps speed signs, one way streets to our left and right and adds information on road condition, all via the iPhone app.

All the shots taken using his iPhone camera are instantly geotagged and uploaded to the TomTom system at the tap of the screen. Each update is then moderated centrally in the same way van data would be. Provided it's accurate, it is then applied to the maps in the next round of updates.

Depending on the type of change and who's uploaded them, these changes can be committed to the maps you and I see within 24 hours. If you've ever cursed the constant calls to update your device, now you know why.

Mapping an island like Martinique, with vans, would normally take a month. In the two hours that we've been driving around we have managed a less impressive twenty updates but despite our limited time on the job, there's a strange feeling in the van that we're changing the world - the virtual one at least.

Over time maps are refreshed, landmarks and points of interest are added and any sudden changes need to be addressed. A great example of this constant need for maintenance and change is when things like Hurricane Irene tears up a road system or when the Olympics rolls into town with its new road layouts for those infamous VIP lanes. In fact there are a staggering 40 million database updates a year keep the big global map up to date.

It's impossible to dismiss the levels of information TomTom has amassed with this approach. In the past 10 years since the first device went on sale, they have collected three-tillion data points, mapped 36 million kilometers of roads, picked up 157 million addresses, 39 million points of
interest across 233 countries.

There is no smart know-it-all machine behind the maps, just a lot of people gathering a lot of data. Well worth bearing in mind next time you're about to scream at your sat nav for asking you to do an unauthorised left turn.