A permanent urban boundary to contain Melbourne's sprawl is part of the new blueprint to deal with the city's booming population, now forecast to hit almost eight million by 2051.

The government's new Plan Melbourne declares the need for a ''clear statement'' on the boundary. But the final line could be different to the existing limits, with the plan setting up a mechanism to determine it.

Source: Department of Transport, Planning and Local Infrastructure

The views of councils, the city's physical features and boundaries formed by major infrastructure are among the factors that will be considered by the new Metropolitan Planning Authority, which will implement the new strategy.

The plan includes sweeping revisions to Melbourne's population, now at 4.3 million, with the city expected to hit 7.7 million people by 2051, up from 6.5 million forecast in the draft of the plan only seven months ago.