Probably you could try to use FSSC (flight simulator scenery creator) which has the flattening switches built into it. (freeware). Can't post the link but any search engine will bring it up or you can check it here. Also Grumpys scenery tutorial will give you some handy tips here. Be careful if you are going to flatten in 'mesh' add-on areas as this can have a roll-on effect especially near the coast. Hope this helps, Bertie