Appraisal Question on Unique Property

[Adam Webb]

I'm looking at 7 acre property with a 29k sqft house on it. (I want to remodel and occupy) The property is obviously worth whatever a developer would pay for the land, knowing that he could make a profit subdividing lots. But an appraiser would not value it that way correct? Do they use any evaluation method other than comps? If they do only use comps, what do they do if there's no comps? Lets say the closest comp is a 3.5 acre property with a 15k sqft house on it. Would the appraiser just double the value? Thanks for your insight!