Policymakers have urged parks professionals to present better green-space data to help them shape election manifestos.
The call came at a policy forum held by Conservative think tank the Policy Exchange in London on behalf of Groundwork UK.
Policy Exchange environment head Guy Newey said green-space data is poor. Ten per cent budget cuts by local authorities in 2010-13 will get worse "but it is hard to work out whether money has been well spent".
The think tank's 2013 Park Land report called for an urban green-space map. Newey said Crawley values 65 out of 103 green spaces at nothing, Rossendale 94 out of 221 at £1 and Basildon values 193ha at £1, which is "obviously nonsense".
He added: "If we don't measure or value what we've got, the chance of impressing people at Westminster is really hard."
A license to access green-space data for London costs £40,000 from Ordnance Survey, which Newey called "obscene". Complex language on applications is a barrier to communities accessing grants, he added.
Lydia Ragoonanan, programme manager at charity NESTA Rethinking Parks, agreed that parks professionals need better data to influence policy. She said they should use US business models such as endowments and consider "parks improvement districts".
Department for Communities & Local Government civil servant Jenny Harland claimed Government responsibility for green spaces at the event after The Parks Alliance representative Bob Ivison said there is "confusion" in Government, with David Cameron's office suggesting Defra governs parks.
Ivison said the Government does not seem to care about parks. "They won't talk to us. The Government has to get its act together."
National Federation of Parks & Green Spaces campaigns officer Dave Morris said the "elephant in the room" is that "30,000 urban green spaces have been plunged into crisis because of underfunding". The lottery has spent £700m on 700 flagship parks but there are 30,000 parks and only 1,500 with Green Flags, he added.
Harland said: "There has been a change about what central Government is doing and the money going into green space, so we're having to look at different ways of achieving things."
There needs to be "a recalibration" in funding streams, she added. "It's not about asking local authorities to protect green-space budgets but doing things differently."
Groundwork chief executive Graham Duxbury said parks professionals "have the evidence we need" to influence policymakers now that "central Government has left the stage". A "genuine flowering of community activity" could influence the policy debate, he added.
Natan Doron, a researcher at Labour policy think tank the Fabian Society, said: "Popular support for parks is what you can sell, not polar bears and climate change."
Forster Communications' Peter Gilheany said NHS clinical commissioning groups are "ripe" to grant cash to parks projects.
BIG Lottery Fund policy partnerships head Chris Butcher said it has given £430m to environmental projects since 2008. He pointed out that although the £57m Changing Spaces fund is ending, the Communities Living Sustainably England and Our Environment Our Future projects are relevant.
The Parks Alliance representative Andrew Gill warned that 7.8 million hectares of state-owned land must remain state-maintained or it will deteriorate.
Changing Spaces - Capacity building
Hall Aitken director Rob Shipway evaluated the performance of Changing Spaces and found "capacity building" - earmarking grant money to help communities by giving free access to consultants, for instance to help interpret planning laws - is important.
He said 92 per cent of 932 groups involved plan to stay together after the end of the project. The groups want to partner with local authorities as "accountable bodies" to manage funding, but cuts mean that one-eighth have struggled to find a suitable partner.