Ah, there's the RUB

A hectare of land on the fringes of Auckland gains almost $13 million in value if it flips to urban zoning, after netting out land development costs. 

From the Infrastructure Commission's latest report:

Figure 3 shows what these differences mean in dollar terms. In Auckland, urban-zoned land is now valued at a premium of nearly $1,300 per square metre relative to nearby rural-zoned land, up from a premium of less than $200 per square metre a decade before. For a 500 square metre residential section, that’s a cost of over $600,000.

Easing up the rules so people can build downtown and in the inner suburbs is great. But the land price gradient for the city should be grounded in paddock costs at the city fringes. It isn't. So land prices throughout the city wind up being out of whack. 

If you want housing affordability, you need to allow cities to grow up and out.

The zoning rent just inside the Auckland boundary is running at $1.3 billion per square kilometer.