This Colombian stamp of 1956 is one of many illustrations that postage stamps have been using as national sovereignity symbols.
This 5 centavos stamp took place in a larger series about the departments of Colombia, viewed through a landscape, an economic activity.
For the San Andrés y Providencia archipelago department, a map played the role, certainly for political reasons. If you click on the link I let you, you can see, on an article of the Wikipedia in English, a map that localized the archipelago at the larger scale of the Caribbean Sea : between the Colombian and Nicaraguan waters.
Since 1822, the possession of these islands by next-to-be Colombia opposed the States that were forming, uniting, dividing themselves in former Spanish Central and Southern Americas. In 1928, the dispute ceased with a treaty, but Nicaragua came back on it in the 1980's. Since 2001, the case is studied by the International Court of Justice.
Digression. In another bloodier case of territorial revendications on islands through stamps and philately : a British reader of Stamp Magazine dated may 2007, accused Argentina to continue its "philatelic propaganda campaign" about Falklands/Malvinas islands. The four stamps qualified were issued JUly 2004 to show four endangered species of fish, which are swimming in these islands' seas...