This interactive route map on Delta.com is the best tool for non-rev travel. You can mouse over any city, click on it and it will show you what flights are non-stop out of that city. (NOTE: Once in the map click on “select map settings” near the top left. Choose “only show nonstop flights”)
You can zoom in/out with tools on left and click/drag the map around.
We have MANY hidden nonstop flights that avoid hubs. Example: JAN-DCA. Please note, not all cities are completely accurate, check them on Travel-Net. I found most are correct. The LAX market has not been completely updated yet with new flights. This map shows flights operated by DL, DL Connection, and some of our worldwide partners – not all.