Which method involves determining one's position on a map by obtaining the grid azimuth to at least two well-defined locations?

The method that involves determining one's position on a map by obtaining the grid azimuth to at least two well-defined locations is known as reselection. This technique is commonly utilized in navigation when a person wants to find their exact position without the aid of GPS or modern technology.

In resection, a navigator identifies two or more prominent landmarks that can be located on the map. By measuring the azimuth (the angle between the north point and the line from the observer to the landmark) to each of these landmarks, the navigator can then plot lines of bearing on the map. The point where these lines intersect indicates the navigator's current location. This method is especially valuable in situations where there are clear landmarks visible and is a fundamental skill taught in map-reading and navigation training.

In contrast, the other methods do not specifically involve determining one's position using a map in this manner. Celestial navigation, for instance, relies on astronomical bodies rather than terrestrial landmarks. Intersection, on the other hand, is the process of determining a location on the map based on the known positions of the observer and specific landmarks, which is not the same as reselection. Polar coordinates refer to a different method of representing points on a plane and are not applicable in this context.