The quality of a map is generally discussed in terms of inches-per-pixel (in/pixel) or centimeters-per-pixel (cm/pixel). Lower inches-per-pixel equals higher map quality. A 1in/pixel map is more detailed than a 2in/pixel map.
High Resolution — 10in/pixel (25cm/pixel)
Very High Resolution— 2in/pixel (5cm/pixel)
Image: Pix4D - GSD in Photogrammetry
Extremely High Resolution - 1in/pixel (2.6cm/pixel)
Lettering and symbols can be easily read. | Image: Drone Deploy - Resolution