Putting aside the urge to chastise the phrase of the day, "disproportionate use of force", the best way to design a new map/variant is to make sure that all nations have multiple options. Forget the trolling nonsense about whether a nation appears stronger than another. The objective in creating a Diplomacy game is into only to give nations a chance to grab an open supply center and get builds in the first year. This of course is the mad rush that players fall into in the game, pausing their commitment to diplomacy until after they 'get them some builds'. They best maps are ones that encourage negotiations most all (nominally seven) players. One of the great things about the standard map is the critical opening moves that need to be discussed, such as English Channel, Burgundy, and Black Sea. Will there be bounces there? Will the be negotiated and planned bounces, or will a DMZ arise? Will someone break the deal on the first turn? Will Austria and Italy go to war immediately or will they both demonstrate trust along the Trieste/Venice border? Will England posture to put it's army into Norway? Will Russia counter that by Sending Moscow to St. Petersburg? Will Turkey send an army into Armenia? That's what gets people talking.

Talking is what makes a Dip game great. I love maps, and my strengths are in tactics. But the game is not chess. It involves multiple players, and multiple relationships. Create a map that gives nations several option to pursue based on their negotiations. Creates something that puts difficult decisions right up front. At the same time allow for flexibility in the game as it moves past the opening few seasons. One of the feature of a great variant/map is that there are options and opportunities for alliance shifts in all phases of the game. Tray to avoid scenarios were the four corner powers have no incentive to do anything but rush the middle. Finally, set victory conditions that allow the map to explore it's potential.