Monetary zones, dollarization and currency boards
Which currency actually circulates in each country, and above all who steers it. The map is political as much as monetary: issuing one's own currency is an attribute of sovereignty that not every state exercises.
Four families: autonomous national currency, shared monetary zone, adoption of a foreign currency (dollarisation, euroisation), and currency board, where the local currency is convertible at a fixed rate backed by reserves.
The colours do not rank from best to worst. Giving up your currency buys stability and credibility, at the price of the ability to devalue or cut rates when the economy turns.
The euro is shared by twenty member states and used de facto by several micro-states and by Kosovo and Montenegro, without any agreement. The two CFA francs peg fourteen African countries to the euro. Ecuador, El Salvador and Panama use the US dollar as their official currency.