Is there a way to see the tangible output of the coverage? How is the author drawing those diagrams? Can I map my room with the strength of wifi signals at dif

Is there a way to see the tangible output of the coverage? How is the author drawing those diagrams? Can I map my room with the strength of wifi signals at different points? I want to do these small hacks but also want to see the change validated in some way. Any pointers will be appreciated.