Location in Diplomacy, or But You're Right Next To Him!
There are several different ways of thinking about the different countries in Diplomacy. The most prevalent is also one of the simplest - two different spheres, the Western (Germany-England-France) and the Eastern (Russia-Turkey-Austria), with Italy in between and three avenues connecting them (northern, central, and southern). This system, which I will call the Dichotomy System because I don't know of any other name for it, results in a playstyle where one nation or alliance of nations from each sphere attempts to gain control of their sphere and then move to the other. It has the advantage of being easy for six of the seven countries - Italy the exception - because, assuming no three-way alliance within the sphere, the direction you need to move most is also the direction in which the most neutral centers lie. France probably has more options in the southwest, but there's no one in that direction, which gives a French player a difficult strategic choice. Italy simply doesn't have any easy choice other than Tunis under this system.
As I said, the main advantage of the Dichotomy System is that the neutral centers and your main rivals are in the same direction at the beginning of the game. The main disadvantage is the same. Under the Dichotomy System, Turkey, Russia, and Austria rush towards the Balkans, France, England, and Italy rush towards Belgium, and Italy is left out in the cold. The problem is that this leaves all six countries vulnerable on their flanks, to varying degrees. Of course, an early move for those flanks would be suicidal if the game is being conducted mainly by adherents of the Dichotomy System, but this is still a glaring weakness.
The second system of playing Diplomacy I've seen is the Central Powers System. First described in Diplomacy World #104, this is apparently peculiar to Maine, and consists of an Austria-Germany-Italy (central) sphere, a Russia-Turkey (eastern) sphere, and an England-France (western) sphere. The advantages of this system are mainly that it is historically accurate and that it is not the Dichotomy System - if the members of the central sphere follow it and the others are prepared for the Dichotomy system, it is often deadly to them. It also doesn't leave Italy the clear odd man out.
The disadvantages of the Central Powers System, however, are more numerous and serious than those of the Dichotomy system. It often leaves Russia and Turkey doomed whether or not they form an alliance, and it requires what is basically a protection racket of France. England, much like Italy under the Dichotomy System, is left out in the cold. It is also far more regimented than the Dichotomy System, and as such far more vulnerable to utter chaos as a result of early stabs.
These are the only formal systems of Diplomacy that I've seen, though I've seen hints that many of the better players of the game do not entirely see the game in terms this simple. The alternative system I would like to propose is far more complicated than either, but presents a far more complete view of the game. I call it the Realpolitik System (RPS), both in tribute to the excellent open-source viewer and adjudicator by Jim Van Verth and in reference to the complex power politics the system gives rise to.
Under the RPS, the board is not divided up into two simple spheres like under the Dichotomy System, or into a cartel and its two boundaries like under the Central Powers System. The starting board consists of no less than seven distinct power groups, each of three members. England, France and Turkey are members of only two power groups, Italy and Russia are members of three, Austria is a member of four, and Germany no less than five (though it is active in two of these only extremely rarely). There are five pairs that are in two spheres together - England-Germany, Germany-Russia, Russia-Austria, Austria-Turkey, and Austria-Italy.
The first or Northwestern power group is centered on Belgium and parallels the Dichotomy System's eastern sphere. It contains England, France, and Germany, and the neutrals Belgium and Holland. All three powers have roughly the same chance at Belgium, were they to commit their full force to this end. However, it requires all three of England's units to do this, and Germany must pass up a significant bargaining chip in the next power group, so though France must delay one of its out-of-sphere neutrals to do so, it generally has the edge. Holland almost always goes to Germany. Alliances between all three powers or any two are possible, though England/Germany is probably the simplest and France/Germany the most powerful.
The second or Northern power group is centered on Skagerrack. It involves England, Germany, and Russia, and the neutrals Denmark, Norway, and Sweden. England has the best chance at Norway and Germany and Russia have equal opportunity to gain Sweden, though Russia generally claims it, because Germany must pass up a significant part of its influence in the Northwestern power group to acquire it. Denmark is nearly always taken by Germany. Alliances between any group of powers are possible, and three-way agreements are more common here than in any other power group. English/German alliances are probably the most powerful, and English/Russian the simplest.
The third or North-Central power group is centered on Warsaw. It encompasses Germany, Russia, and Austria and no neutral supply centers. For the latter reason, it is often ignored in the early game. It is very rare that this power group is marked by anything other than a three-member nonaggression pact, though German/Austro-Hungarian alliances occasionally form and anything is possible.
The fourth or Eastern power group parallels the Eastern sphere in the Dichotomy System and is centered on Rumania. It contains Russia, Turkey, and Austria-Hungary, and the neutral Rumania. Russia has an edge in bringing force to bear on Rumania and generally takes it, though a united effort by Turkey and Austria-Hungary can deprive the bear of it. Russian/Turkish alliances are by far the most prevalent, powerful, and simple in this sphere, with Russia taking Rumania and then assisting Turkey in the Southeastern power group.
The fifth or Southeastern power group is centered on Greece. It involves Turkey, Austria-Hungary and Italy, and the neutrals Greece, Bulgaria, and Serbia. Austria-Hungary has the most force to bring to bear on Greece and as such usually takes it, though the dual monarchy committing that much force to this power group is by no means guaranteed. Turkey almost always claims Bulgaria and Austria-Hungary is nearly guaranteed Serbia. Thanks to the Lepanto, Italian/Austro-Hungarian alliances are the most prevalent in this power group, though Turkey/Austria-Hungary is more powerful and Italian/Turkish alliances are simpler.
The sixth or Central power group is the focus of the Central Powers System and is centered on Tyrolia. It encompasses Austria-Hungary, Italy, and Germany, and no neutral supply centers. Germany almost always stays neutral or weakly against anyone who claims Tyrolia early in this sphere. An Italian/Austro-Hungarian war and nonaggression pact are almost equally likely, and nearly always depend on events in the Southeastern power group.
The seventh or Southwestern power group is centered on Piedmont. It contains Italy, Germany, and France, and the neutrals Tunis, Spain, and Portugal. Tunis almost always goes to Italy, and Spain and Portugal to France. North Africa, if included as a supply center, often goes to Italy even though France can get there faster, and makes the game and this group in particular much more interesting. A nonaggression pact is far more likely here than a war, though war is far more likely if North Africa is included. The only even remotely common alliance is between Italy and Germany.
The Realpolitik System leads to a far more intense and complex game of Diplomacy than either the Dichotomy System or the Central Powers System. The most interesting change when adopted is that it becomes common for countries to work together in one area and against each other in another - England, for example, will often work with Germany in the North-Central power group but with France in the Northwestern. It also gives Austria and Germany much better chances, as they are more often courted aggressively by those neighbours who share two power groups with them instead of plotted against. It also allows for both very standard play (according to either the Dichotomy or Central Powers system) and nonstandard (Austro-Hungarian/Russian action against Germany) without being considered outside the scope of the system. It also encourages conversation with every player in the game, for even if (as Russia) Italy and France are not members of any of your power groups, they each are in power groups with two or three countries which are, and this applies to nearly every country. Perhaps the Realpolitik System's most glaring disadvantage is that it allows for a variety and level of play that can be extremely disorienting to new Diplomacy players, such as myself, or those familiar to excess with either of the other systems. However, RPS provides a frame of reference by which nearly any strategy by any country or group of countries can be understood, a frame which is otherwise lacking.