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You can throw the ball down once, but if you bounce off a wall, you can see the ball bouncing back and forth between the two parties since the transverse corridor. Radio waves do that too, only more like this: A part of the wave goes straight down the hall, but each edge of the wave bounces between the walls. The part of the wave is moving directly towards the corridor when the first antenna and the signals will bounce milliseconds later. The network card is smart enough to know that while you receive the same transfer again, only one copy of the transfer used.

As a column casts a shadow on the path of a flashlight beam, the obstacles in the way of an RF wireless transmission of generated shadows. If you have an antenna mounted on the access point a column of the building, the air in the rear of the column in the shadow of the RF.

Heavy walls and doors to mute or dampen the signal, reflecting metal or bounce the signal back. RF signals can not penetrate metal. Materials that are porous absorb the signal energy, materials high in water content also absorbs the signal. Back to the analogy of the pebble beaches in the water, the radio waves sometimes skips like a stone on the surface of the water and end up beyond what would be a normal range.

You can see that it is in the area to be mapped, the most complex of the survey. As an inspector, you should ensure that they have large (but not too much) coverage in a given area.