When you sail along the continental margin by boat, you can determine your latitude and longitude coordinates with a star locator at regular intervals, and then connect them and mark them on the map, which becomes a local map.
There used to be a lot of blank areas.
With more and more navigators, there are fewer and fewer blank places on the world map after the nautical charts of Dagmar, Barents, Davis and Bering.
World War II can basically draw all major war zones. Before the Japanese invaded China, they sent a large number of scientific research teams to draw a military map of China in the name of geographical exploration of minerals.
After the emergence of satellite remote sensing photography technology, the global map can be drawn very accurately.