The value of residential land has surged across Sydney in the past year but the strongest gains have been concentrated in the city's west.

Figures released by the NSW Valuer-General on Thursday show the total value of land across the state climbed to $1.34 trillion last year.

Land values increased by well over 10 per cent in almost all Sydney council areas, though the fastest increase was in Blacktown, where the median value of a residential plot climbed 47 per cent.

"We've got attractive things, but affordability would still have to be the main factor," said Terry Comino, principal of Ray White Blacktown, when asked to explain the increase in land values in the area.