There are many factor effecting Radio wave:
Shadowing – Terrain or Buildings partially reducing signal.
Attenuation - Strength of signal is reduced when passing through a building.
Diffraction – a signal can bend around an object to a limited extent.
Reflection – this reduces signal strength but may also aid coverage
By making perfectly planned network we can use Tall building for us as advantage as well.
http://www.planningni.gov.uk/dcan14_annex_c