There are almost as many Republican delegate allocation formulas as there are states. For our map, we've grouped into five categories with the goal being to place each of the 50 states, 5 territories, and Washington D.C. into the category that best fits based on our somewhat superficial understanding of the rules. For the finer points, visit Greenpapers or FHQ.
In the description below, 'states' is meant to also include the territories and DC.
Proportional: This method of allocation awards delegates in some way proportional to the vote. For some states, it is a single allocation based on the statewide vote, while others do it by individual Congressional District, with some remainder allocated statewide. Some states have a minimum threshold to receive any delegates. Per Republican Party rules, a proportional allocation method is required prior to March 15, with South Carolina excepted. However, some states work around this using a Threshold allocation.
Threshold: This method of allocation is in some way proportional to the vote, unless a single candidate exceeds a predetermined amount, when it generally becomes Winner Take All. Most of the states in this category vote prior to March 15, and it is a way to get around the RNC proportional allocation requirement. The threshold is 50% in most places (2/3 in Tennessee) with most states applying it at both the individual Congressional District and statewide.
Winner Take All (Split): Generally, each individual Congressional District has a vote, with the winner getting that District's delegates. There are also some delegates allocated on a Winner Take All basis across the entire state. Pennsylvania fits into this category, but it is worth noting that it involves voting for delegates directly. There are other states (e.g., Illinois) that do this as well, but in Pennsylvania the delegates are not bound to any particular candidate.
Winner Take All: The cleanest allocation method. You win the most votes, you get all the state's delegates.
Other: States that select delegates through a caucus/convention process, often lasting several weeks. The delegates chosen are generally not bound to a particular candidate.