There will be less space to eat your lunch in a park, less room to take your dog for a walk and less chance of securing a spot to play in a sporting field.

These are some of the ramifications of the rapidly increasing population in Sydney's inner city, which is not being matched by a similar increase in the supply of parks and open space, a City of Sydney report shows.

Sydney's Prince Alfred Park, one of the green spaces close to the city. Many more such spaces will be needed as the population surges. Credit:Janie Barrett

Over the next 15 years the amount of total open space per person in the city is expected to shrink by more than 20 per cent, from 18.3 square metres a head to 14.4 square metres by 2036.

By that stage the Sydney local government area will be home to an extra 81,000 people, up from 200,000 now.