Sir Tim Berners-Lee said he was delighted by the decision
Mapping agency Ordnance Survey (OS) has launched a service offering free and unrestricted access to most of its map data.
After months of public consultation, OS OpenData was launched on 1 April by Communities Secretary John Denham.
He said he hoped it would attract "a new wave of entrepreneurs" to reuse the data in innovative ways.
However Ramblers, the walkers group, has expressed disappointment that OS' paper maps have not been included.
"We are very disappointed that the walkers maps have been left out of it," said a spokesperson from the group.
The group had lobbied for the inclusion of the paper map ranges - called Explorer and Landranger - during the consultation, he added.
The maps retail for up to £15 in shops and walkers describe them as essential guides.
Guardian newspaper journalist and campaigner for free data Charles Arthur agreed that the omission made OS OpenData "not quite all we hoped for" but said that overall he was very impressed with the initiative.
"It's going to be the acid test of how making a product free can expand the market and generate new commercial services. We view it as a big win for the Free Our Data campaign," he told BBC News.
Ordnance Survey said the decision to leave out the paper maps was "in the national interest".
"There was concern that by giving away the 1:25,000 and 1:50,000 maps you would undermine the continued provision of a nationwide paper map series," said a spokesperson.
"It is in the national interest to have a nationwide paper map."
OS OpenData exists alongside an earlier data sharing scheme called OS OpenSpace, which is also available for free but operates with limitations.
In the past people have used it to create safe cycling routes, as well as maps detailing local post and phone boxes.
OS OpenData has been funded by the government and is the result of the "Making Public Data Public" initiative announced by PM Gordon Brown in November 2009.
Web creator Sir Tim Berners-Lee and Professor Nigel Shadbolt, two key figures behind data.gov.uk, a project to open up almost all data acquired for official purposes, welcomed the move.
"I'm delighted that the Ordnance Survey is releasing this data for free re-use," said Sir Tim.
Mr Denham said the new scheme placed the UK at the "cutting edge of a digital revolution".
"The changes signal a wider cultural change in Government based on an assumption that information should be in the public domain unless there is a good reason not to - not the other way around," he added.
"Greater openness, accountability and transparency in Government will give people greater choice and make it easier for individuals to get more directly involved in issues that matter to them."