I haven't made a map (yet

) but I think I can help you, you see that tool up on your top menu thingy? It should look like an cross with arrows going up down and left and right. click your model and righltclick on the arrow thing, that's your move tool you can move objects around by typing numbers in the boxs inthe tool of you want your map directyl center in the Z,Y,X coordinates just delet everything in all the boxs and make them 0 that puts it exactly center Z is up and down and X and Y are the other ways.
Now If your fixing open edges I don't know if this si the right way to fix em but, click your model, right click, click convert to editable mesh, click the face icon then go to create on your toolbar (should be on the right side of screen) then click on a vertex you want to be the side of the face click on another vertex you want to be the other side then finally click one last vertex. This should create a new face and fill in the open edge, if it looks totaly black you might have to redo it in a different order.
IDK if this is how I saw something earleir on this, but this is how I fix edges like that when I model.