25ft of entrace located near corner of building

Does the 25ft referring to a straight line measurement? Or, it's following the building footprint? Or, as a radius? The reason of this question being an existing ashtray is located at the corner of our building, while the main entrance is located at ~10ft from the corner on the other side. Historically, the designated smoking area is vaguely located where the ashtray is. As we are making the Entrance Area a smoke-free zone, would this very ashtray be exempt due to its location at the other side of the corner?