The process used to create your map could also be a problem. I remember some methods I took had this issue as well; now I rarely use blur filters--and even when I do, only in controlled areas (ex: if you select an area then blue it, only the interior space will blue, not the edges where blurring is the most noticable.)

Perhaps that helps? If you explain how you created the image maybe we can find another manner that does not rely upon blur filters, brushes, and such.