Since you didn't post your coverages it's hard to tell what is happening here, but it looks like you pay via your mortgage escrow which they sometimes overcharge. If you only have an empty lot you should lower your coverages to liability only. I just got my renewal and it went from $1200 yearly to $250 as a result.
You also should make sure you are taking advantage of any discounts they offer. I get a discount for having a computer science degree, having home and auto through the same company, and there is even a discount for having a Costco membership.