bird's-eye survey

The direct distance across the island was less than three miles, and by a bird’s-eye survey from the highest point in the centre, they calculated that the most practicable path would be about five miles.

However, thinks I, this is owing to my taking a horizontal view, instead of a bird's-eye survey.

Having searched the flat without finding him, Elizabeth went to the window, with the intention of making a bird's-eye survey of the street.