I looks like you made a box and filled it with stuff, which is not really a good way to build a level. An inevitable result of this method is that there is soo much open unused space (and of course, that the map boundaries is a big box).
Next time you decide that you want to make a whole new map, you should try to start somewhere (could be a control point) and just add on to that and keep building and building onto that until you have a level where the areas, the points of interest and even the map boundaries reflects the considerations you made while making the map.