This method of navigation, with moving map, use as references the ground radio stations (commercial and/or aviation NDB’s) and localization is based on Automatic Direction Finder (usual we can find two of ADF systems on every aircraft).
The main advantage of this system is revealed by not using the satellite constellation (GPS, GLONASS or GALILEO) or VOR stations.

Principle
Because ground stations are well positioned (x, y as latitude and longitude), using an ADF system controlled by a computer, we can determine the aircraft position in 2D space, considering the error from propagation and accuracy of ADF. The radial can be determined by ADF

(see figure 1 and 2).

X_AC=f(ro1, ro2, … , ron, x1, x2, … , xn, y1, y2, … , yn)±epsilon_x
Y_AC=f(ro1, ro2, … , ron, x1, x2, … , xn, y1, y2, … , yn)±epsilon_y

where:

ro1, ro2, … , ron represent determined angle by ADF to ground station
x1, x2, … , xn represent latitude position of ground stations
y1, y2, … , yn represent longitude position of ground stations
epsilon_x and epsilon_y represent error

(see figure 3)

After XAC, YAC determination, using a digitized map stored in a computer, can place the aircraft in position. Anyway, using the determined coordination, a flight plan can be easly produced and followed.