If you plot the lot size (x axis) vs assessed value (y-axis), and fit a line to the (noisy) data, the y-intercept will tell you the implicit value of having a buildable lot of any size.

The pattern you see is totally typically. The marginal value of one additional sq ft is generally less than the average.

Example: let’s say you had 0.25 acres and your neighbor had 1 acre, and you were allowed to bargain for land on the border. Ignoring ability to pay, you’d probably value each marginal square foot more than your neighbor- they already have the space they need for a patio, swingset, chicken coop, yard.