Akamai, a huge content delivery network (CDN), regularly publishes statistical data on various aspects of Internet connection in the world. Their 2015 Q1 report contains, among many other interesting data, a table of average Internet connection speed by country, which I visualized in the following map:
Akamai describe the methodology they use in a blog post. The most important thing to notice is that they measure the maximum download speed of every unique IP address in each country but cannot tell how many users share Internet access under one public IP address.
Thus, one should correlate the map above with the following map (also based on the aforementioned report), which shows the number of unique IPv4 addresses per 100 inhabitants—lower numbers indicate that either fewer people have Internet access or more people share one Internet connection, which makes it effectively slower for each of them: