Wired on Friday: Geoff Chase jogs past every house in his local Detroit neighbourhood, down every street, around every traffic island. At the end of his daily promenades, he transfers a package of data from a small pocket device to his desktop PC. Soon, his computer has a perfect, 3D streetmap of his area, traced out by his wanderings.

Over two months, Amsterdam inhabitants are offered the same device, which they carry around as they walk about the city. The compiled data from all the participants forms not only a map of the city, but a plot of pedestrian and car traffic, of hourly activity and even of the effect of weather on how the city behaves. Their cumulative track is shown in real-time on a high-resolution display in the centre of the city - slowly building from a few wandering lines into a familiar and detailed map of the town.

A bunch of ramblers in London take a day-long walk around the city. They document everything they see, tagging its precise location with the same equipment Chase and the Amsterdammers use. They call it documenting psychogeography. It's another original map.

All use the same little gadgets, a GPS unit. The cheapest cost about $150 (€128).

They're used by ramblers, lost drivers and, in this case, amateur mapmakers.

For all of these people, charting the places where they live is a hobby. But the technology they are using is militarily precise, discovering its owner's precise location by triangulating from a network of US military satellites. These cartographers are, in their own way, building as detailed and up-to date a gazetteer as many professional offerings of even the recent past.

It's just another example of new technology turning a pursuit that was previously restricted to professionals into a domain at which anyone can have a bash. Desktop publishing amateurised chunks of the printing industry. The Web amateurised barrel loads of professions, from publishing to radio broadcasting to, with pornography, the oldest profession of all.

By reducing the costs of tools and instruments, and by providing access to those tools to anyone with a yen, all these industries were radically affected. They found themselves hosting an Open Day for hobbyists that never quite ended.

This time, it's the turn of the geographic information system (GIS) industries.

GIS is a multibillion dollar industry with strong bases in Ireland and with good growth prospects. Perhaps they shouldn't worry too much.

Amateurisation rarely has the catastrophic effect predicted on a profession. For every printer who lost a job to desktop publishing, dozens found their copy shop businesses booming from PC users bringing in camera-ready artwork.

And while every trade despairs of the drop of quality amateurisation brings, it also heralds an influx of new talent, who have an easy way to get started and an early incentive to excel.

But amateurisation does shake things up and upset the more conservative professionals. Right now, I imagine there's people in the GIS community who see these new experimenters as fringe enthusiasts, like radio hams or train-spotters are viewed by their "host" professions.

But they'd be wrong to ignore what's happening. While mapping your local neighbourhood doesn't benefit many, compiling and adding your data with those of others creates a more generally useful map. Especially when, like all enthusiasms, it's given away free for anyone to use.

And while trying to achieve that grand project, the geolocation fans are also building their own tools - free systems for checking for errors, protocols for pooling data, and ways of attaching notes and names to geographical locations.

All of these tools and datasets are, of course, already available amongst GIS professionals - for a price.

Some, particularly those developed by academics, are cheap and finely crafted. But some are not. And many are tied up with restrictive licences or over-protectively designed not to work with other tools.

In a small market, where everyone knows one another and everyone has a budget, it's easy to get away with substandard work or pricey markups. But when you're surrounded by a crowd of hobbyists with no money and a lot of time, things can get very competitive, very fast.

But it might not be the private sector of the GIS market that should worry.

From all appearances, it'll be the government-run GIS world that will get the real shake-up.

One of the reasons why the amateurs are being so meticulous in their mapping, and so keen to collaborate with each other, is that basic mapping data is still so expensive.

It's not so bad in the US, where government-sourced data (as so much mapping data is), is provided free to anyone with an interest. The argument, so it goes, is that the taxpayers have already paid for this data so why should they pay again?

Even such expensively collected data as NASA's radar topography dataset - which gives the height of almost every part of the earth's surface to 90 and 30 metre resolutions - is available for free.

Here, however, government mappers have more of an obligation to make a buck than to serve the public. The Irish Ordnance Survey makes more than €4 million annually selling its government-collated mapping data, and has been criticised in the past for its overly commercial viewpoint (and in recent years, has even suffered a fraud scandal over mislayed receipts and altered cheques).

The same is true of many "half-privatised" government cartographers in other countries.

Without free and public sources of data, the new GIS amateurs have to start from scratch.

That's bad for them. And, given the thousands of small and profitable industries that usually spring forth from the amateurisation process, bad for the countries that do not encourage them.

Right now, thousands of amateur cartographers in the US are inventing cheap new ways of using all this data and furiously experimenting with the latest technology. Their cost-saddled in this and other countries are slowly following suit.

And in a few years time, as Moore's Law grinds relentlessly on, those GPS gadgets of theirs will go from costing a few hundred dollars to being, as the saying goes, "given away in packets of Cornflakes". Or at least present on every mobile phone, as telco companies plan.

When that happens, there'll be a new demand for mapping data, and a new demand for GIS. We'll all be amateur mappers then.

Will that new audience be happy to pay high fees for professionally produced, monopoly data. Or will they be turning to the free information made by their predecessors?