I am not a developer either but a City Planner. I use this number to see what parts of town are under preforming.
In one section on Main Street a lot of the improvement values are less than the Land Value. For example one has a 7,500 sqft building on it with an improvement value of $140,100 and a land value of $272,500. https://www.assessment.cot.tn.gov/RE_Assessment/ParcelDetailIMPACT.aspx23
This area is zoned for Commercial only. As an Urban Planner I recognize that this is a location that is not zoned correctly. Placing a more flexible zoning district on the land that would allow for a mix of uses is good for the property owner and for the City. In this case the ratio is negative and is pretty obvious.
I had a rezoning once that had a few really strong NIMBY opponents . When I looked at my ratio map I noticed that the only people that spoke against the rezoning had put a lot of money into their own houses (better than 10:1 ratio) but all of the other housing in the neighborhood sat at about 2:1 and needed to be redeveloped or rezoned. The rezoning failed despite my recommendation.
I run the numbers for the whole city at once using the tax data but in some areas like farmland it is not useful.