You make a good point, except that in many areas there are no comparable land sales. This is especially true of urban areas. How would you value a townhouse lot on .05 acres or less, when typically the developer bought the land in bulk? The same is true of most quarter acre lots for detached homes in subdivisions, which is a typical lot size in my state. Again, few if any sales. Besides, if I went by your method, I'd essentially be doing a separate land appraisal for every property I appraise. When I do a large, rural lot, I generally do check, unless I'm confident I know land values in the area, which are usually consistent with assessed values