How is the distance between the project site and the manufacturing location determined for Materials...

The distance between the project site and the manufacturing location is determined by the straight line distance. This is because the LEED v4 Reference Guide for Building Design and Construction states that the distance should be measured as the crow flies1. The straight line distance is the shortest distance between two points on a plane, regardless of the mode of transportation or the road conditions. The image that you sent shows the straight line distance between the project site and the manufacturing location as the line segment AB.