The new London Gardens Online website is part of a three-year project by the London Parks and Gardens Trust to compile an easily-accessible database of all the 2,500 spaces researched for its inventory since 1995.
So far, 421 of the sites are online at the new site, with the rest to be added in the next six months.
By 2011, the website will contain further information on each of the sites, including contemporary and historical photos.
London Parks and Gardens Trust chairman Chris Sumner explained: "This is the largest project that the Trust has undertaken and its most important achievement since it was launched as an independent charitable trust at the Chelsea Flower Show in May 1994. The Inventory builds on the aims of the Trust which endeavours to increase the knowledge and appreciation of parks, squares, gardens, cemeteries, churchyards - all those places that form London's open space network."