Tip: Are you a non-native English speaker? I have just finished creating a 
Web AppParticipants of the Eurobarometer 386 survey (organized by the European Commission) answered various questions about their knowledge of foreign languages. One of the questions was whether they speak any English, and if yes, whether their English is very good, good, or basic.
To visualize their responses and provide a rough measure of English proficiency, I decided to assign numerical values to the options. In the following map, “very good” is worth 10, “good” is 7, “basic” is 3, and “do not speak” is 0. The value “3” for “basic” may seem rather low, but I believe that communication with a person who has only basic command of any given language may be problematic compared to people with good knowledge, hence the value.
Of course, the index depends primarily on the number of people who speak any English at all. This is what the following map shows:
