I specialize in vacant land.
@Account Closed - I'm not sure what you are referring to here, but this year I made $143k on a single property flip after only owning it for a few months. I flip a lot of vacant land, the key is to buy right. Maybe you are referring to what I call "making it developer ready", in that case there can be some unknowns and it can take a while to get though the upgrades and enhancements for the planning department, utilities, roads, etc... But the payoff her is usually huge, again; assuming you buy right.
@Account Closed - You are correct if you are referring to land in CA. CA has had Prop 13 on the books for many years and that limits the % increase that can be applied to land until a new property transfer transaction happens. However, there are many states and the counties that reevaluate land values each year. Some states and counties keep the assessed value to a percentage of the market value (e.g. 20% to 80%), some attempt to get at full market value, it really just depends. I have bought and sold land in 6 different states in the last year and they all have different ways to assess land. In SOME places the assessed value can be very different from the actual market value of the property; in others it is usually very close.
@Account Closed mentioned, look into the details of the sales and see if they are buying blocks of lots or single lots.