As the other commenter responded, I'm referring to the linguistic, socioeconomic and judicial homogeneity. Even though the US is culturally diverse, it still has a single currency, a single dominant language and a single jurisdiction (with minor state specific legal requirements). I only need one US visa to travel to all 52 states. A software company taking payments in the US has access to all 52 states. A peach cobbler is called the same throughout the US even though the recipe might change a little bit from place to place.
This is not the case in Africa or Europe, where countries use different languages, scripts, legal codes, currencies, driving directions, etc...
EDIT: I'm referring the land masses included in the visualization and what they entail in practical terms.
The US can be seen as a single market, the same applies to China and India. Europe has the schengen area, the EU and the EEA. Africa needs similar initiatives.