“Developable” value is undeveloped land value. Land would have very little value if it couldn’t be developed. (Leaving out the case of land with natural resour

“Developable” value is undeveloped land value. Land would have very little value if it couldn’t be developed. (Leaving out the case of land with natural resources to mine, or otherwise enjoy or extract, but little or no development potential.) Developing land, by adding utility infrastructure, building structures, adding building amenities and aesthetic improvements, landscaping etc, all require new sunk costs, which then also increase taxes. So the return on that property investment will have to cover not only its own cost, but the increase in taxes they create. It is essentially buying something (development), then being asked to rent it forever (the tax on the increased property value). A pure land tax would not tax property improvements directly, and so would make development much easier to pay for itself. While making holding undeveloped land much more expensive (given total taxes across all real estate remain the same, with a higher land only tax, and zero tax on the property development).